A VNC client implemented entirely in HTML5, using WebSockets and Canvas. Supports encrypted connections. Remotely manage servers without having to install extra software!
Kickstart is an HTML5 framework which makes it easier to build websites. It's a collection of HTML5, CSS, image elements,, and JavaScript templates which give you a head start on setting a page up. All you have to do is include two JavaScript files and a CSS file. Mobile friendly, too. Includes lots of different buttons, icons, and styles.
MDwiki is a single-page wiki engine implemented as an HTML5 page with JavaScript. Drop a bunch of Markdown documents into a directory, add a copy of mdwiki.html, and you now have a fully functional wiki. You can't edit it with your web browser but it's fine as a mostly static CMS or a documentation site.
A chart and diagram webapp written in HTML5 that lets you do pretty much whatever Lucidchart does. Export to PNG, GIF, and JPEG.
HTML5 SIP client. Written in Javascript, throw it onto a page and configure it to contact a SIP gateway of some kind. Uses webRTC built into all modern web browsers. Does audio as well as video. Can contact the PSTN if the gateway can.
Github repo: https://github.com/DoubangoTelecom/sipml5
A venerable FOSS SIP client with many possible user interfaces, include an HTML5 one that uses javascript. Also has a CLI version
A streaming audio server written in python, optimized for small devices. HTML5 front-end so you don't need a special client to control or listen to it, just a modern browser. Built in indexing database. Based on CherryPy and jPlayer.
Somebody reimplemented WinAMP in HTML5 and Javascript. Runs in your browser. Skin compatible. Local sound files can be played by dragging and dropping. Can be doubled in size. UI is very close to the original WinAMP. Can be embedded in another website.