It's for a small source viewing utility on the site, that allows users to view Thacmus and Thacsite (the website for Thacmus) page sources. I implemented this to back a few of the tutorials and show some of the pieces of Thacmus in work, and if a user just wanted to browse through the Thacmus source and not download it, they could peruse through it on there.
You can see the source of the source viewer here:
http://deadimp.org/thacsite/?page=source&file=page/source.php&ajax=1 (putting it ajax mode has it output in plain text which doesn't use highlight_file(), so it works that way).
I've been looking at forum software, and I've briefly used SMF while testing a few out (I've installed it for my school's band website [as a discussion place for officers only], though it hasn't been used). I'm considering the main set, and maybe bbpress. Though, I'm sure I could get somewhere near the functionality of bbpress with a little work.