The Linux port for APUS (Amiga PowerUp Systems) was started in 1997 with support from Phase5 who provided 3 developer boards to Jes Sørensen, Roman Zippel and Jesper Skov.
Initially it seemed that the proprietary information needed to make the port would make a bad mix with the open source model of Linux. Indeed, it postponed the public release of Linux/APUS somewhat, but it all worked out in the end. Phase5 have approved all the released information and, sparse commenting aside, all source code changes are freely available.
I refer to the following ports of Linux in this document:
Linux/m68k The port for the Motorola MC68k CPU family. This is what you would use for running Linux on an Amiga without PowerUp. It is also the port that Linux/APUS is based on, since all the drivers are the same.
Linux/PPC The port for the Motorola PowerPC CPU family. The home of this port is at www.linuxppc.org. This port has multi-machine support, including PMAC, PREP, CHRP and partially APUS.
Linux/APUS The port targeted at Amigas with Phase5's PowerUp hardware. With time, it will be a proper part of Linux/PPC. It may also become a base for the support of PowerPC cards from other Amiga vendors.