suppleText is a very flexible and elegant wiki focused on semantics, clean aesthetics, web standards, usability, and giving users the power to customize the presentation of the wiki. suppleText is free and open source (under the GPL)! Check out some sites using suppleText!
This site is currently being set up as the community site with which development of suppleText will occur. Stay tuned!
In the meanwhile, check out the FormattingRules and play in the SandBox.