Gobby is a free collaborative editor supporting multiple documents in one session and a multi-user chat. It runs on Microsoft Windows, Mac OS X, Linux and other Unix-like platforms. It uses GTK+ 2.6 as its windowing toolkit and thus integrates nicely into the GNOME desktop environment. Gobby is also very promissing in area of XP – eXtreme Programming, because it can ease pair programming. 

 Features

• Realtime Collaboration through encrypted channels (version 0.4.0 and up)
• Each user has its own changeable colour to be identified by others
• IRC-like chat for communicating with your partners while coding
• Syntax highlighting for most programming languages
• Session password protection
• Multiple documents in one session
• Drag'n'drop of documents into Gobby
• Document synchronisation on request
• Zeroconf support
• Unicode support
• Cross-platform: runs on Microsoft Windows, Linux, Mac OS X (albeit not natively) and other flavours of UN*X
• Gobby is free software and licenced under the GPL 2