ZPUino is an implementation of the 32-bit Open Source ZPU processor. It is a small implementation that is meant to be used with the Arduino IDE. It is capable of speeds up to 100Mhz and can run on the Papilio Platform.
The AVR8 Soft Processor is an Open Source RISC processor that implements all the registers and instructions of an ATmega103 processor. It supports the avr-gcc toolchain for compilation of ANSI C code.