The picotux 100 is the world's smallest Linux computer, only slightly larger (35mm×19mm×19mm) than an RJ45 connector. Inside, there is an ARM7 CPU at 55 MHz running uClinux kernel 2.4.27 and Busybox 1.0. Two communication interfaces are provided, 10/100 Mbit half/full duplex Ethernet and a serial port with up to 230.400 baud. Five additional lines can be used for either general input/output or serial handshaking.  http://www.picotux.com/