The nice guys at devio.us are offering free (or cheap premium) shell accounts on openbsd servers.
Free linux shells are everywhere, but I haven't seen OpenBSD shell accounts offered, at least for free, in recent memory. I manage an OpenBSD shell/tunneling/irc/whatever server for members of CCCKC, but it's not "free" so much as it's one of the many benefits and shared resources that come with being a paid member of our hackerspace.
Their policy is pretty straight-forward. If you pay $2 or $3 per month, you get a premium account that allows you to background a couple of processes, gives you a larger file quota, and the ability to create more databases. Regular accounts may not background processes or run a detached screen after logging off, only get one mysql database, and 100MB of storage space. Oh heck, just grok the services page.