Realtime collaborative editing for WordPress content, powered by Etherpad Lite.
This plugin requires Etherpad installed on a server, so you can't get this working just by sticking it in the plugins folder. However, this plugin is super-useful, so for certain uses it's worth the effort. Fans of PiratePad will appreciate it, and indeed anyone who wants to enable collaborative editing in WordPress. Great for conference and course websites, for instance.