Plan9 is a distributed operating system from Bell Labs.
To get at them here, you'll need to prefix the command with 9, e.g.
$ 9 rc // will launch rc, plan9's shell $ 9 9c // will launch plan9's c compiler $ 9 grep // will launch plan9's flavor of grep, etc.
For a full list of the stuff you can use, see plan9port's documentation (linked below). Plan9port includes some graphical applications, too, namely sam and acme -- if you can figure out how to use 'em over ssh, go nuts!