Squad is a web-based collaborative code editor.

Web conferencing that just works. Dimdim provides easy, open, affordable collaboration. Use for online meetings, eLearning, desktop sharing, training, distance education, unified collaboration, webinar, free web meetings and more.

SIMILE is focused on developing robust, open source tools that empower users to access, manage, visualize and reuse digital assets. Learn more about the SIMILE project.

A really cool collaboration tool for any web page. Post notes, draw and even chat with others. The sandbox is really interesting to play around with

A nice flash based Visio style application. Not all the features available yet, but something to keep an eye on.