ucLinux is a new kernel forked from linux 2.0. The main difference is doesn't require a MMU in the processor. This is good and bad: It allows linux to be ported to more architectures, like 68000 and Coldfire. However, without an MMU, ucLinux provides no security against malicious or buggy binaries.

This linux can run on routers, palm pilots, and single board computers the size of a SIMM

Relevant URLs:

http://uclinux.org  (The OS itself)
http://uclinux.com  (they sell a ucSimm computer that runs ucLinux)
http://openhardware.net

See also: ucSimm, Motorola Dragonball, EZ328SIMM, Kiwi