diff --git a/doc/TODO.md b/doc/TODO.md
index 7dec2265..33ccd93e 100644
--- a/doc/TODO.md
+++ b/doc/TODO.md
@@ -21,6 +21,8 @@
  - build a very basic interface with
  	- a start/stop sync button
  	- a room list sorted alphabetically
+ - do some preprocessing on sync response which can then be used by persister, summary, timeline
+ - support timeline
  	- clicking on a room list, you see messages (userId -> body)
  - send messages
  - fill gaps with call to /messages
@@ -28,3 +30,4 @@
  - lazy loading members
  - decide denormalized data in summary vs reading from multiple stores PER room on load
  - allow Room/Summary class to be subclassed and store additional data?
+ - store account data, support read markers
diff --git a/src/event-emitter.js b/src/EventEmitter.js
similarity index 100%
rename from src/event-emitter.js
rename to src/EventEmitter.js
diff --git a/src/matrix/room/room.js b/src/matrix/room/room.js
index 1fadccaf..5d4fcd98 100644
--- a/src/matrix/room/room.js
+++ b/src/matrix/room/room.js
@@ -1,21 +1,28 @@
 import RoomSummary from "./summary.js";
 import RoomPersister from "./persister.js";
+import EventEmitter from "../../EventEmitter.js";
 
-export default class Room {
-	constructor(roomId, storage) {
+export default class Room extends EventEmitter {
+	constructor(roomId, storage, emitCollectionChange) {
+        super();
 		this._roomId = roomId;
 		this._storage = storage;
 		this._summary = new RoomSummary(roomId);
 		this._persister = new RoomPersister(roomId);
+        this._emitCollectionChange = emitCollectionChange;
 	}
 
 	async applySync(roomResponse, membership, txn) {
-		this._summary.applySync(roomResponse, membership, txn);
+		const changed = this._summary.applySync(roomResponse, membership, txn);
 		this._persister.persistSync(roomResponse, txn);
+        if (changed) {
+            this.emit("change");
+            (this._emitCollectionChange)();
+        }
 	}
 
 	load(summary, txn) {
 		this._summary.load(summary);
 		return this._persister.load(txn);
 	}
-}
\ No newline at end of file
+}
diff --git a/src/matrix/session.js b/src/matrix/session.js
index 49b6b7cf..49019ed3 100644
--- a/src/matrix/session.js
+++ b/src/matrix/session.js
@@ -1,11 +1,12 @@
 import Room from "./room/room.js";
+import ObservableMap from "../observable/map.js";
 
 export default class Session {
 	constructor(storage) {
 		this._storage = storage;
 		this._session = null;
 		// use Map here?
-		this._rooms = {};
+		this._rooms = new ObservableMap();
 	}
 	// should be called before load
 	// loginData has device_id, user_id, home_server, access_token
@@ -37,13 +38,18 @@ export default class Session {
 		}));
 	}
 
+    get rooms() {
+        return this._rooms;
+    }
+
 	getRoom(roomId) {
-		return this._rooms[roomId];
+		return this._rooms.get(roomId);
 	}
 
 	createRoom(roomId) {
-		const room = new Room(roomId, this._storage);
-		this._rooms[roomId] = room;
+        const updateCallback = (params) => this._rooms.update(roomId, params);
+		const room = new Room(roomId, this._storage, updateCallback);
+		this._rooms.add(roomId, room);
 		return room;
 	}
 
@@ -61,4 +67,4 @@ export default class Session {
 	get accessToken() {
 		return this._session.loginData.access_token;
 	}
-}
\ No newline at end of file
+}
diff --git a/src/matrix/sync.js b/src/matrix/sync.js
index 61659820..542b64b4 100644
--- a/src/matrix/sync.js
+++ b/src/matrix/sync.js
@@ -3,7 +3,7 @@ import {
 	HomeServerError,
 	StorageError
 } from "./error.js";
-import EventEmitter from "../event-emitter.js";
+import EventEmitter from "../EventEmitter.js";
 
 const INCREMENTAL_TIMEOUT = 30000;
 const SYNC_EVENT_LIMIT = 10;
@@ -117,4 +117,4 @@ export default class Sync extends EventEmitter {
 			this._currentRequest = null;
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/observable/map.js b/src/observable/map.js
new file mode 100644
index 00000000..e2044410
--- /dev/null
+++ b/src/observable/map.js
@@ -0,0 +1,55 @@
+import BaseObservableMap from "./map/BaseObservableMap.js";
+
+export default class ObservableMap extends BaseObservableMap {
+    constructor(initialValues) {
+        super();
+        this._values = new Map(initialValues);
+    }
+
+    update(key, params) {
+        const value = this._values.get(key);
+        if (value !== undefined) {
+            this._values.add(key, value);
+            this.emitChange(key, value, params);
+            return true;
+        }
+        return false;   // or return existing value?
+    }
+
+    add(key, value) {
+        if (!this._values.has(key)) {
+            this._values.add(key, value);
+            this.emitAdd(key, value);
+            return true;
+        }
+        return false;   // or return existing value?
+    }
+
+    remove(key) {
+        const value = this._values.get(key);
+        if (value !== undefined) {
+            this._values.delete(key);
+            this.emitRemove(key, value);
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    reset() {
+        this._values.clear();
+        this.emitReset();
+    }
+
+    get(key) {
+        return this._values.get(key);
+    }
+
+    get size() {
+        return this._values.size;
+    }
+
+    [Symbol.iterator]() {
+        return this._values.entries()[Symbol.iterator];
+    }
+}
diff --git a/src/observable/map/BaseObservableMap.js b/src/observable/map/BaseObservableMap.js
new file mode 100644
index 00000000..dc7c7199
--- /dev/null
+++ b/src/observable/map/BaseObservableMap.js
@@ -0,0 +1,66 @@
+import MapOperator from "./operators/MapOperator.js";
+import SortOperator from "./operators/SortOperator.js";
+
+export default class BaseObservableMap {
+    constructor() {
+        this._handlers = new Set();
+    }
+
+    emitReset() {
+        for(let h of this._handlers) {
+            h.onReset();
+        }
+    }
+    // we need batch events, mostly on index based collection though?
+    // maybe we should get started without?
+    emitAdd(key, value) {
+        for(let h of this._handlers) {
+            h.onAdd(key, value);
+        }
+    }
+
+    emitChange(key, value, ...params) {
+        for(let h of this._handlers) {
+            h.onChange(key, value, ...params);
+        }
+    }
+
+    emitRemove(key, value) {
+        for(let h of this._handlers) {
+            h.onRemove(key, value);
+        }
+    }
+
+    onSubscribeFirst() {
+
+    }
+
+    onUnsubscribeLast() {
+
+    }
+
+    subscribe(handler) {
+        this._handlers.add(handler);
+        if (this._handlers.length === 1) {
+            this.onSubscribeFirst();
+        }
+        return () => {
+            if (handler) {
+                this._handlers.delete(this._handler);
+                if (this._handlers.length === 0) {
+                    this.onUnsubscribeLast();
+                }
+                handler = null;
+            }
+            return null;
+        };
+    }
+
+    map(mapper, updater) {
+        return new MapOperator(this, mapper, updater);
+    }
+
+    sort(comparator) {
+        return new SortOperator(this, comparator);
+    }
+}
diff --git a/src/observable/map/Operator.js b/src/observable/map/Operator.js
new file mode 100644
index 00000000..e17f63d8
--- /dev/null
+++ b/src/observable/map/Operator.js
@@ -0,0 +1,22 @@
+// import BaseObservableMap from "./BaseObservableMap.js";
+
+export default class Operator /* extends BaseObservableMap */ {
+    constructor(source) {
+        // super();
+        this._source = source;
+    }
+
+    onSubscribeFirst() {
+        this._sourceSubscription = this._source.subscribe(this);
+    }
+
+    onUnsubscribeLast() {
+        this._sourceSubscription();
+        this._sourceSubscription = null;
+    }
+
+    onRemove(key, value) {}
+    onAdd(key, value) {}
+    onChange(key, value, params) {}
+    onReset() {}
+}
diff --git a/src/observable/map/operators/FilterOperator.js b/src/observable/map/operators/FilterOperator.js
new file mode 100644
index 00000000..84b3336c
--- /dev/null
+++ b/src/observable/map/operators/FilterOperator.js
@@ -0,0 +1,55 @@
+import Operator from "../Operator.js";
+
+export default class FilterOperator extends Operator {
+    constructor(source, mapper, updater) {
+        super(source);
+        this._mapper = mapper;
+        this._updater = updater;
+        this._mappedValues = new Map();
+    }
+
+    onAdd(key, value) {
+        const mappedValue = this._mapper(value);
+        this._mappedValues.set(key, mappedValue);
+        this.emitAdd(key, mappedValue);
+    }
+
+    onRemove(key, _value) {
+        const mappedValue = this._mappedValues.get(key);
+        if (this._mappedValues.delete(key)) {
+            this.emitRemove(key, mappedValue);
+        }
+    }
+
+    onChange(key, value, params) {
+        const mappedValue = this._mappedValues.get(key);
+        if (mappedValue !== undefined) {
+            const newParams = this._updater(value, params);
+            if (newParams !== undefined) {
+                this.emitChange(key, mappedValue, newParams);
+            }
+        }
+    }
+
+    onSubscribeFirst() {
+        for (let [key, value] of this._source) {
+            const mappedValue = this._mapper(value);
+            this._mappedValues.set(key, mappedValue);
+        }
+        super.onSubscribeFirst();
+    }
+
+    onUnsubscribeLast() {
+        super.onUnsubscribeLast();
+        this._mappedValues.clear();
+    }
+
+    onReset() {
+        this._mappedValues.clear();
+        this.emitReset();
+    }
+
+    [Symbol.iterator]() {
+        return this._mappedValues.entries()[Symbol.iterator];
+    }
+}
diff --git a/src/observable/map/operators/MapOperator.js b/src/observable/map/operators/MapOperator.js
new file mode 100644
index 00000000..ee4118e4
--- /dev/null
+++ b/src/observable/map/operators/MapOperator.js
@@ -0,0 +1,55 @@
+import Operator from "../Operator.js";
+
+export default class MapOperator extends Operator {
+    constructor(source, mapper, updater) {
+        super(source);
+        this._mapper = mapper;
+        this._updater = updater;
+        this._mappedValues = new Map();
+    }
+
+    onAdd(key, value) {
+        const mappedValue = this._mapper(value);
+        this._mappedValues.set(key, mappedValue);
+        this.emitAdd(key, mappedValue);
+    }
+
+    onRemove(key, _value) {
+        const mappedValue = this._mappedValues.get(key);
+        if (this._mappedValues.delete(key)) {
+            this.emitRemove(key, mappedValue);
+        }
+    }
+
+    onChange(key, value, params) {
+        const mappedValue = this._mappedValues.get(key);
+        if (mappedValue !== undefined) {
+            const newParams = this._updater(value, params);
+            if (newParams !== undefined) {
+                this.emitChange(key, mappedValue, newParams);
+            }
+        }
+    }
+
+    onSubscribeFirst() {
+        for (let [key, value] of this._source) {
+            const mappedValue = this._mapper(value);
+            this._mappedValues.set(key, mappedValue);
+        }
+        super.onSubscribeFirst();
+    }
+
+    onUnsubscribeLast() {
+        super.onUnsubscribeLast();
+        this._mappedValues.clear();
+    }
+
+    onReset() {
+        this._mappedValues.clear();
+        this.emitReset();
+    }
+
+    [Symbol.iterator]() {
+        return this._mappedValues.entries()[Symbol.iterator];
+    }
+}
diff --git a/src/observable/map/operators/SortOperator.js b/src/observable/map/operators/SortOperator.js
new file mode 100644
index 00000000..aacc29e2
--- /dev/null
+++ b/src/observable/map/operators/SortOperator.js
@@ -0,0 +1,119 @@
+import Operator from "../Operator.js";
+
+/**
+ * @license
+ * Based off baseSortedIndex function in Lodash <https://lodash.com/>
+ * Copyright JS Foundation and other contributors <https://js.foundation/>
+ * Released under MIT license <https://lodash.com/license>
+ * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
+ * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ */
+function sortedIndex(array, value, comparator) {
+    let low = 0;
+    let high = array.length;
+
+    while (low < high) {
+        let mid = (low + high) >>> 1;
+        let cmpResult = comparator(value, array[mid]);
+
+        if (cmpResult > 0) {
+            low = mid + 1;
+        } else if (cmpResult < 0) {
+            high = mid;
+        } else {
+            low = high = mid;
+        }
+    }
+    return high;
+}
+
+// TODO: this should not inherit from an BaseObservableMap, as it's a list
+export default class SortOperator extends Operator {
+    constructor(sourceMap, comparator) {
+        super(sourceMap);
+        this._comparator = comparator;
+        this._sortedValues = [];
+        this._keyIndex = new Map();
+    }
+    
+    onAdd(key, value) {
+        const idx = sortedIndex(this._sortedValues, value, this._comparator);
+        this._sortedValues.splice(idx, 0, value);
+        this._keyIndex.set(key, idx);
+        this.emitAdd(idx, value);
+    }
+
+    onRemove(key, _value) {
+        const idx = sortedIndex(this._sortedValues, value, this._comparator);
+        this._sortedValues.splice(idx, 0, value);
+        this._keyIndex.set(key, idx);
+        this.emitAdd(idx, value);
+    }
+
+    onChange(key, value, params) {
+        // index could have moved if other items got added in the meantime
+        const oldIdx = this._keyIndex.get(key);
+        this._sortedValues.splice(oldIdx, 1);
+        const idx = sortedIndex(this._sortedValues, value, this._comparator);
+
+    }
+
+    onSubscribeFirst() {
+        this._sortedValues = new Array(this._source.size);
+        let i = 0;
+        for (let [key, value] of this._source) {
+            this._sortedValues[i] = value;
+            this._keyIndex.set(key, i);
+            ++i;
+        }
+        this._sortedValues.sort(this._comparator);
+        super.onSubscribeFirst();
+    }
+
+    onUnsubscribeLast() {
+        super.onUnsubscribeLast();
+        this._sortedValues = null;
+    }
+
+    onReset() {
+        this._sortedValues = [];
+        this.emitReset();
+    }
+
+    get length() {
+        return this._source.size;
+    }
+
+    [Symbol.iterator]() {
+        return this._sortedValues;
+    }
+}
+
+//#ifdef TESTS
+export function tests() {
+    return {
+        test_sortIndex(assert) {
+            let idx = sortedIndex([1, 5, 6, 8], 0, (a, b) => a - b);
+            assert.equal(idx, 0);
+            idx = sortedIndex([1, 5, 6, 8], 3, (a, b) => a - b);
+            assert.equal(idx, 1);
+            idx = sortedIndex([1, 5, 6, 8], 8, (a, b) => a - b);
+            assert.equal(idx, 3);
+        },
+
+        test_sortIndex_reverse(assert) {
+            let idx = sortedIndex([8, 6, 5, 1], 6, (a, b) => b - a);
+            assert.equal(idx, 1);
+        },
+
+        test_sortIndex_likeArraySort(assert) {
+            const a = [5, 1, 8, 2];
+            const cmp = (a, b) => a - b;
+            a.sort(cmp);
+            assert.deepEqual(a, [1, 2, 5, 8]);
+            let idx = sortedIndex(a, 2, cmp);
+            assert.equal(idx, 1);
+        }
+    }
+}
+//#endif
diff --git a/src/live-collections/live-map.js b/src/observable/misc.js
similarity index 71%
rename from src/live-collections/live-map.js
rename to src/observable/misc.js
index beb3b1c7..4b30d0f1 100644
--- a/src/live-collections/live-map.js
+++ b/src/observable/misc.js
@@ -1,6 +1,4 @@
-import EventEmitter from "./event-emitter.js";
-
-class LiveMap {
+class ObservableMap {
 	constructor() {
 		this._handlers = new Set();
 	}
@@ -30,43 +28,46 @@ class LiveMap {
 		}
 	}
 
+    onSubscribeFirst() {
+
+    }
+
+    onUnsubscribeLast() {
+
+    }
+
 	subscribe(handler) {
 		this._handlers.add(handler);
+        if (this._handlers.length === 1) {
+            this.onSubscribeFirst();
+        }
 		return () => {
 			if (handler) {
 				this._handlers.delete(this._handler);
+                if (this._handlers.length === 0) {
+                    this.onUnsubscribeLast();
+                }
 				handler = null;
 			}
 			return null;
 		};
 	}
-
-	[Symbol.iterator]() {
-
-	}
 }
 
-class Operator extends LiveMap {
+class Operator extends ObservableMap {
 	constructor(source) {
 		super();
 		this._source = source;
 	}
 
-	subscribe(handler) {
-		this.onSubscribe(this._source);
-		let subscription = super.subscribe(handler);
-		let sourceSubscription = this._source.subscribe(this);
-		return () => {
-			sourceSubscription = sourceSubscription && sourceSubscription();
-			subscription = subscription && subscription();
-			// this.onUnsubscribe(); ?
-			return null;
-		};
-	}
+    onSubscribeFirst() {
+        this._sourceSubscription = this._source.subscribe(this);
+    }
 
-	onSubscribe() {
-
-	}
+    onUnsubscribeLast() {
+        this._sourceSubscription();
+        this._sourceSubscription = null;
+    }
 
 	onRemove(key, value) {}
 	onAdd(key, value) {}
@@ -74,7 +75,7 @@ class Operator extends LiveMap {
 	onReset() {}
 }
 
-export default class LiveMapCollection extends LiveMap {
+export default class ObservableMapCollection extends ObservableMap {
 	constructor(initialValues) {
 		super();
 		this._values = new Map(initialValues);
@@ -124,7 +125,7 @@ export default class LiveMapCollection extends LiveMap {
 	}
 }
 
-class LiveMapOperator extends Operator {
+class ObservableMapOperator extends Operator {
 	constructor(source, mapper, updater) {
 		super(source);
 		this._mapper = mapper;
@@ -132,13 +133,6 @@ class LiveMapOperator extends Operator {
 		this._mappedValues = new Map();
 	}
 
-	onSubscribe(source) {
-		for (let [key, value] of source) {
-			const mappedValue = this._mapper(value);
-			this._mappedValues.set(key, mappedValue);
-		}
-	}
-
 	onAdd(key, value) {
 		const mappedValue = this._mapper(value);
 		this._mappedValues.set(key, mappedValue);
@@ -162,6 +156,19 @@ class LiveMapOperator extends Operator {
 		}
 	}
 
+    onSubscribeFirst() {
+        for (let [key, value] of this._source) {
+            const mappedValue = this._mapper(value);
+            this._mappedValues.set(key, mappedValue);
+        }
+        super.onSubscribeFirst();
+    }
+
+    onUnsubscribeLast() {
+        super.onUnsubscribeLast();
+        this._mappedValues.clear();
+    }
+
 	onReset() {
 		this._mappedValues.clear();
 		this.emitReset();
@@ -172,12 +179,12 @@ class LiveMapOperator extends Operator {
 	}
 }
 
-class FilterOperator extends LiveMapOperator {
+class FilterOperator extends ObservableMapOperator {
 
 }
 
 class SortSet {
-	constructor(liveMap) {
+	constructor(ObservableMap) {
 
 	}
 }
@@ -188,4 +195,4 @@ export function tests() {
 
 		},
 	};
-}
\ No newline at end of file
+}
diff --git a/src/ui/web/ListView.js b/src/ui/web/ListView.js
new file mode 100644
index 00000000..ba4f230f
--- /dev/null
+++ b/src/ui/web/ListView.js
@@ -0,0 +1,78 @@
+import * as html from "./html.js";
+
+class UIView {
+    mount(initialValue) {
+
+    }
+
+    unmount() {
+
+    }
+
+    update() {
+
+    }
+}
+
+export default class ListView {
+    constructor(collection, childCreator) {
+        this._collection = collection;
+        this._root = null;
+        this._subscription = null;
+        this._childCreator = childCreator;
+        this._childInstances = null;
+    }
+
+    getDOMNode() {
+        return this._root;
+    }
+
+    mount() {
+        this._subscription = this._collection.subscribe(this);
+        this._root = html.ul({className: "ListView"});
+        this._childInstances = new Array(this._collection.length);
+        for (let item of this._collection) {
+            const child = this._childCreator(item);
+            this._childInstances.push(child);
+            const childDomNode = child.mount();
+            this._root.appendChild(childDomNode);
+        }
+        return this._root;
+    }
+
+    unmount() {
+        this._subscription = this._subscription();
+        for (let child of this._childInstances) {
+            child.unmount();
+        }
+        this._childInstances = null;
+    }
+
+    onAdd(i, value) {
+        const child = this._childCreator(value);
+        const childDomNode = child.mount();
+        this._childInstances.splice(i, 0, child);
+        const isLast =  i === this._collection.length - 1;
+        if (isLast) {
+            this._root.appendChild(childDomNode);
+        } else {
+            const nextDomNode = this._childInstances[i + 1].getDOMNode();
+            this._root.insertBefore(childDomNode, nextDomNode);
+        }
+
+    }
+
+    onRemove(i, _value) {
+        const [child] = this._childInstances.splice(i, 1);
+        child.getDOMNode().remove();
+        child.unmount();
+    }
+
+    onMove(fromIdx, toIdx, value) {
+
+    }
+
+    onChange(i, value) {
+        this._childInstances[i].update(value);
+    }
+}
diff --git a/src/ui/web/html.js b/src/ui/web/html.js
new file mode 100644
index 00000000..0335ca69
--- /dev/null
+++ b/src/ui/web/html.js
@@ -0,0 +1,43 @@
+export function setAttribute(el, name, value) {
+    el.setAttribute(name, value);
+}
+
+export function el(elementName, attrs, children) {
+    const e = document.createElement(elementName);
+    if (typeof attrs === "object") {
+        for (let [name, value] of Object.entries(attrs)) {
+            setAttribute(e, name, value);
+        }
+    }
+    if (Array.isArray(children)) {
+        // TODO: use fragment here?
+        for (let c of children) {
+            e.appendChild(c);
+        }
+    }
+    return e;
+}
+
+export function text(str) {
+    return document.createTextNode(str);
+}
+
+export function ol(... params)      { return el("ol", ... params); }
+export function ul(... params)      { return el("ul", ... params); }
+export function li(... params)      { return el("li", ... params); }
+export function div(... params)     { return el("div", ... params); }
+export function h1(... params)      { return el("h1", ... params); }
+export function h2(... params)      { return el("h2", ... params); }
+export function h3(... params)      { return el("h3", ... params); }
+export function h4(... params)      { return el("h4", ... params); }
+export function h5(... params)      { return el("h5", ... params); }
+export function h6(... params)      { return el("h6", ... params); }
+export function p(... params)       { return el("p", ... params); }
+export function strong(... params)  { return el("strong", ... params); }
+export function em(... params)      { return el("em", ... params); }
+export function span(... params)    { return el("span", ... params); }
+export function img(... params)     { return el("img", ... params); }
+export function section(... params) { return el("section", ... params); }
+export function main(... params)    { return el("main", ... params); }
+export function article(... params) { return el("article", ... params); }
+export function aside(... params)   { return el("aside", ... params); }