A version of Linux designed to run on the MIPS architecture. It works on most MIPS machines and has two flavors: big-endian (mipseb) and little-endian (mipsel). The big endian version runs on a variety of SGI machines, and there's a distribution called HardHat based on Red Hat. The distribution is pretty comprehensive, but the platform still lacks a good X server. The little endian runs on some non-SGI mips based machines. Most programs work with a simple compilation of the source. Debian is also supposed to be working on a distro for mips.

My adventures into the world of mips linux started when I received a free SGI Indy from the CS department at RIT. It came without a copy of Irix, and I didn't feel paying $600 for a licence. After a few weeks of work and a lot of frustration, I've gotten the box to do something so it's no longer a rather expensive doorstop.

Linux Mips resources:

Linux on SGI/MIPS: http://www.linux.sgi.com/
Linux/MIPS FAQ: http://lena.fnet.fr/
Simple Linux/MIPS: http://foobazco.org/~wesolows/Install-HOWTO.html