AROS is an Open Source porting/rewriting of AmigaOS 3.1 aimed at various platform. Main target is Intel architecture, nonetheless it exist AROS portings for ARM, Motorola 68000, and a PPC version too, even if it usually catches less interest than the others.
Infact there is no native PPC version of AROS. It should run hosted into PPC Linux Flavours or Mac PPC Darwin.
http://en.m.wikibooks.org/wiki/Aros/Platforms/PPC_support