Etherpad

Etherpad Lite V1.1.1 

is a collaborative editor, sort of like a web-based multiplayer Notepad but with some really amazing features and a really developer-friendly community and framework. Etherpad Lite is completely open-source and comes with no douchery whatsoever attached..

• http://etherpad.org/

Plugins of interest

• Integration with Moodle, Elgg, MediaWiki and others!
• Linkify - adds internal links to etherpad lite. This great plugin written by FourPlusOne means you can easily link pads together giving Etherpad Lite more of a wiki style feel. To link pads together use the foo syntax.
• Speech-to-Pad - You can now talk straight into a pad on Etherpad Lite. This functionality is supported in Chrome only at current however more browsers are expected to support this soon.
• jQuery - ideal for injecting pads into your web pages and reading contents.
• More plugins

What’s next?

We have achieved our goal of making etherpad easy to adopt for web developers, we’re really happy with the number of contributors and new plugins being developed by the community. Our next goals are:

• Provide a robust testing framework
• Migrate any legacy Etherpad instances (such as PrimaryPad, PiratePad) to Etherpad Lite
• Language translation support
• Integration with even more CMS’

Etherpad as Wiki

• hybrid wiki-etherpad tool built with DokuWiki (downloadable open-source)
• Cunidu Etherwiki How-to
• Hackpad "is the best wiki ever" (hosted)