The world’s most popular wiki software is developed for the Wikipedia project but available for free under open source license.
Tools (3)
Wetpaint is a hosted wiki service.
According to Wikipedia : Wikispaces is a hosting service (sometimes called a wiki farm) based in San Francisco, California. Launched in March 2005, Wikispaces is owned by Tangient LLC and is among the largest wiki hosts, competing with PBworks, Wetpaint, and Google Sites (formerly JotSpot).