See http://jot.andstuff.org/. Some highlights:
- Full XHTML compliance.
- Written in Python.
- Uses a home-grown memory-mapped object store as the PageDatabase. This is not only fast, but it allows the code to be simplified greatly, as objects in the store require no instantiation.
- A WikiPedia-style diff engine (also donated to MoinMoin).
- Rudimentary support for authentication and access control lists to control permissions for pages and page trees. Fully-open wikis with no UserName authentication are supported as a trivial subcase of this functionality.
This engine is presently in use at AndStuffWiki.
The Jotwiki -- see http://www.jotwiki.net/ . Some highlights:
- Written in Java.
- source code is GPL and can be downloaded from sourceforge.
- stores wiki page data in text files.
- support for access control lists and CAPTCHA.