Markdoc - Markdoc is a lightweight Markdown-based wiki system.
Zim Wiki - Zim is a graphical text editor used to maintain a collection of wiki pages. Each page can contain links to other pages, simple formatting and images.
TiddlyWiki - a non-linear personal web notebook
Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.
VoodooPad - VoodooPad is a personal wiki developed for the Mac OS. It lets users create a personal wiki by giving them the ability to manage a network of pages right from the desktop.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.