Wikis
PBwiki
PB works is the world's largest provider of hosted business and educational workspaces.
Wet Paint
Wetpaint lets you build a rich, online community around the whatever-it-is that you’re really into. Utilizing the best features of wikis, blogs, forums and social networks, Wetpaint mixes everything you need so you can create, collect, and organize content on your own social website.
WikiHow
A collaborative writing project to build the world's largest user-generated "how-to" manual.
Wikipedia
Wikipedia is an online encyclopedia edited primarily by anonymous contributors.