I have recently been playing with carl’s new project, http://codegolf.com/
Basically the idea is to solve given programming challenges in as few characters as possible. The output from entries is compared to a reference output and any that pass the comparison are scored by the number of characters they used. Some challenges require you to parse input aswell.
The implementation is quite neat. Code you upload is run as an unprivileged user inside a chroot inside a jail in FreeBSD, and the whole lot is re-created for every run. Four languages are available, Ruby, PHP, Perl and Python with brainfuck (wikipedia entry) support promised soon.
Anyway, if you have a spare afternoon/evening/week it is pretty good fun.
If that sounded like an advert it wasn’t meant to :)