TWiki is an open source enterprise wiki
The TWiki web site is "http://twiki.org/". TWiki is fairly full featured. It can support multiple wiki "webs", useful for separate groups or separate projects. When installed it includes a fair amount of online user documentation in one of the preconfigured "webs". TWiki is written in Perl. TWiki is designed to work with Apache, but apparently people run it with other web servers. The TWiki source code can be downloaded from the TWiki web site, which appears to be running TWiki. A lot of developer documentation is there, and there are a number of people who monitor that site to answer questions. Even with all that there are still a number of questions that are asked about TWiki here on stackoverflow.com.
