A very interesting wiki I just discovered: http://en.literateprograms.org/LiteratePrograms:Welcome
They allow you to post source code of any computer program in any language, comment it, etc. They have a very neat extension which allows you to download a tarball of all the programs documented on a particular page. The code can be broken up into pieces so that individual sections of a program can be discussed in more detail. The pieces on a page can then be associated with files using an internal transclusion.
The extension pieces the stuff together again. It also does syntax highlighting for a lot of languages.
I'm posting this to textbook-l and wikipedia-l because I know there are a lot of computer programming related pages on both wikis that could make use of this resource. Given the URL, the project also seems to be aiming for multilinguality. I actually think it would make a nice addition to the Wikimedia project family, if a bit specialized.
Erik