Koding is a website that provides a limited amount of FTP-accessible storage (I think around 4GB? Maybe 2GB?) and a limited VPN to use for Web development. I think it supports SSH access, but I've only used the in-browser shell. Last I checked, long-running processes don't survive between shell sessions.
On the other hand, it supports CGI-style websites based on PHP, Ruby, and some other languages. These pages can stay online forever.
Koding was previously open-signup under the name Kodingen, but it didn't have any support for shell access at that time. Nevertheless, I successfully ran shell commands via PHP and Ruby scripts, and this was enough to test out Racket and Arc programs.
Not too long ago I removed my Arc installation from my Koding account. Racket was taking up too much disk space, and http://tryarc.org was enough for me. :) I'm pretty sure the potential is still there if someone's interested.