The OpenBIOS project provides you with most free and open source Open Firmware implementations available. Here you find several implementations of IEEE 1275-1994 (Referred to as Open Firmware) compliant firmware.
Among its features, Open Firmware provides an instruction set independent device interface. This can be used to boot the operating system from expansion cards without native initialization code.
It is Open Firmware's goal to work on all common platforms, like x86, AMD64, PowerPC, ARM, Sparc and Mips. With its flexible and modular design, Open Firmware targets servers, workstations and embedded systems, where a sane and unified firmware is a crucial design goal and reduces porting efforts noticably.
Open Firmware is found on many servers and workstations and there are several commercial implementations from SUN, Firmworks, CodeGen, Apple, IBM and others.
In most cases, the Open Firmware implementations provided on this site rely on an additional low-level firmware for hardware initialization, such as coreboot or U-Boot.