PukiWiki ('PoohKeyWeKey' without any prolonged sounds) is a wiki implementation that works on PHP 4 and 5, outputs XHTML 1.1, has many plugins (including one for bug tracking) and skins (such as one for embedded browsers), enables English and/or UTF-8 configuration, and features case-insensitive WikiNames. The formatting rules are based on YukiWiki.
Devalot is a social networking application centered around software projects. It connects the user community with the development community and encourages participation and communication. It includes all the features you've come to expect in modern Web-based applications such as tagging, comments, and a wiki, as well as features you'd expect in project tracking software such as ticketing. It has features similar to some of those found in Trac, Collaboa, GForge, Mephisto, and Typo.