You can also install MediaWiki, the software used for Wikipedia, with LaTeX support, on your own server (say, your own domain or a department server);
http://www.mediawiki.org/wiki/MediaWiki
Possibly useful for things like a study group for problem sessions or a textbook where multiple people work on the same problems, which not only helps to spread solutions but also to practice writing mathematics where others will see it. If you need to copy the code for some reason then you can just view the page wiki code.
This may also be useful for departments to keep track of their various seminars. Any attendee of the seminar could post their notes on a wiki. A collaborative, published effort may increase interest, especially amongst the undergraduates and graduate students.