codepad
Those of you who write computer programs might be interested in my latest project: http://codepad.org/.

It's a pastebin that runs your code for you. My idea is that this will be good for showing people how to do things, demonstrating errors and weird behavior, and solving small problems when you don't have an interpreter/compiler handy. Untrusted code is run under a supervisor based on geordi. It uses ptrace, chroot, and resource limits to jail the untrusted code in a way that is probably still not as airtight as I'd like.

If there's a language or feature that would make codepad more useful to you, please request it, and I'll do my best to accommodate.