Implementations in Web browsers

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

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
Client-side session and persistent storage implemented in Firefox 2, IE 8
Custom content handlers partially implemented in Firefox 2
ping attribute implemented in Firefox 3
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

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.