Do you know what wikis are? According to Wikipedia, the king of all wikis, a wiki is usually a collaborative website which can be edited by anyone with access to it!
Wikis have many applications, including sharing of knowledge within organizations or communities with specific interests. You can find a wiki on just about any subject! Just try a search on Wetpaint or wiki.com to look for subject-specific wikis.
You want to build your own wiki? PeanutButterWiki, Wetpaint, and Wikia are some of the most popular free wiki services that allow you to create your own wiki community. Teachers, you can try to set up a wiki for the courses you teach! For more information on such services, you may see Wikipedia’s List of wiki farms.