Tiki also works great as a web-based collaboration tool. Tiki is a multi-purpose package with a lot of native options and sections that you can enable/disable as needed. It is designed to be international, clean and extensible.
Tiki incorporates all the features present in several excellent wiki systems available today plus many new features and options, allowing you flexibility in the design of diverse applications from a single point of entry--whether you want a simple wiki or a complex site offering a variety of services to a whole user community.
You can use Tiki as a forums site, a chatroom, for poll taking, customer support site and much more! And, Tiki is under active development so the possibilities are endless.
You can see some NiceSites or Other Tiki sites in action.
Major features include -
A File/Image Gallery,
Banner Management System,
Mobile Tiki (Pda And Wap Access),
Theme Control Center,
Acls, And More.
A full feature list is available on the developers web site.