Implementations in Web browsers

List of known implementations of HTML 5 in web browsers (list is incomplete, feel free to extend it)

For an interactive view of features and which browsers they work in, see http://a.deveria.com/caniuse/

HTML 5

canvas with some limitation implemented in Firefox, Opera, Safari, and Konqueror 4, with ExplorerCanvas emulated in Internet Explorer
getElementsByClassName implemented in Firefox 3, Safari 3.1, Opera 9.5
localStorage and sessionStorage implemented in Firefox 2, IE 8, nightly WebKit
Database storageimplemented in Safari
Custom content handlers partially implemented in Firefox 2
ping attribute implemented in Firefox 3 (turned off by default) - note the implementation does not reflect the latest changes in the specification
cross-document messaging implemented in Opera 9, Safari and Firefox 3, IE 8
Audio interface implemented in Opera 9, Konqueror 4, Safari 3.1
video element implemented in Safari 3.1 and Firefox 3.1 alfa 2, basic implementation in experimental Opera build; with mv_embed script in every browser with Java support
Server-sent DOM events implemented in Opera 9
contenteditable attribute implemented by Opera, Internet Explorer, Safari and Firefox 3
Drag & drop (partially) implemented in Internet Explorer, Safari and Firefox nightly builds.
event DOMContentLoaded implemented in Firefox, Safari, Opera
Web Workers partly implemented in Firefox 3.1 alfa 2
Offline Web applications implemented in Chrome (via Gears plugin), latest Safari on iPhone and Firefox 3.1

Project webforms2 emulates a big part of WF2 in every browser
date input element with input-type-date works in Firefox, IE6/7, Safari
Repetition Model - Opera 9 (native), with repetitionmodel works in Firefox, IE6/7, Safari 2.0.4
Project [1] emulate in IE6/7 validation, date and time types, range, repetition, calculated fields, datalist, autofocus.

Not yet.