MediaWiki is a free software wiki package originally written for Wikipedia. It is now used by several other projects of the non-profit Wikimedia Foundation and by many other wikis, including this very website, the home of MediaWiki.
activeCollab is an easy to use, web based, open source collaboration and project management tool.
GoToMeeting : Web conferencing, Online Meetings, Net Meeting, Online Training, Web Conference, Presentation Software, Web conferencing solution, Web collaboration, Web conferencing service, Collaboration software, Web Conferencing Software