• 37signals
  Simple software to help you get organized
  Goodbye to bloat. Simple, focused software that does just what you need and nothing you don't
  in Software > tools with collaboration organized web by 30 users
• Apache Wave
  Welcome to Apache Wave (incubating)
  in Web > tools with apache collaboration opensource wave
• co-meeting - A new style of group communication
  co-meeting is a text-based group discussion tool to renovate web conference and information sharing.
  in Web > tools with collaboration conference sharing
• cTuning.org
  cTuning.org is a community-driven collaborative Mediawiki-based portal that brings together industry, academia and IT users to optimize programs and architectures collectively and build smart self-tuning adaptive computing systems based on statistical and machine learning techniques.
  in Web > reference with adaptive collaboration community learning machine optimization wiki
• Forterra Systems
  Forterra Systems provides virtual world software that enable our customers and partners to create their own secure and scalable collaborative 3D Internet solutions. Our customers can meet, collaborate, train, communicate, experiment, and socialize over any network with a better experience and lower cost than common alternatives.
  in Software with 3dweb collaboration development platform virtual world by 3 users
• hackpad
  wiki
  in Web > tools with collaboration online wiki
• Imagination Cubed
  whiteboard
  in Web with collaboration drawing by 9 users
• Katalabs
  We grew out of research into architecting and building projects on the open source Sirikata platform at Stanford. Katalabs was founded with the humble goal of taking this work to scale. We believe the web can be made better through real-time, synchronized collaboration and communication environments built at the intersection of 2D and 3D. These will be delivered through the browser you already use and loaded by simply clicking a link. We are building the tools that will make that possible.
  in Software with 3d 3dweb collaboration virtual world
• Lotus Greenhouse
  Lotus Greenhouse is a live community website where you can use Lotus Collaboration Products for free! Join the community to exchange ideas, collaborate with others, and share information on innovation and collaborative products.
  in Software with collaboration free live lotus trial by 2 users
• Metafilter
  Metafilter is a weblog that anyone can contribute a link or a comment to.
  in Web > news with collaboration community news weblog by 33 users
• Ohloh
  Ohloh is a resource for open source intelligence on thousands of open source projects. Ohloh collects software metrics from a variety of sources including the project’s source code and the software development infrastructure used by the project’s development team.
  Ohloh is an open source directory that anyone can edit. It features comprehensive metrics and analysis on thousands of open source projects.
  in Software with collaboration opensource by 23 users
• OpenStreetMap
  OpenStreetMap is a free editable map of the whole world. It is made by people like you. OpenStreetMap allows you to view, edit and use geographical data in a collaborative way from anywhere on Earth.
  in Web > reference with collaboration map opensource wiki by 41 users
• reddit.com
  reddit is a source for what's new and popular online. reddit learns what you like as you vote on existing links or submit your own!
  in Web > news with collaboration news by 102 users
• Rizzoma — communicate and collaborate in realtime
  in Web > tools with collaboration opensource wave by 2 users
• ShiftSpace
  an open source browser plugin for collaboratively annotating, editing and shifting the web.
  in Web with collaboration web2.0 by 4 users
• Slashdot
  News for nerds, stuff that matters
  in Web > news with collaboration news by 213 users
• Thinkature
  Real-time collaboration for the web
  in Software > tools with collaboration mindmapping real-time web by 19 users
• Wiggio
  Makes it easy to work in groups.
  in Web > tools with collaboration web2.0 by 4 users

collaboration from all users