After spending a few months as a download available only to YDL.net members, Yellow Dog Linux 3.0.1 ISOs are now freely available. The distro now includes HFS+ support and the 2.4.22-based kernel.
Other distros that run on Apple hardware include Debian for PPC, Debian for Motorola 680×0, Gentoo PPC, Mandrake Linux 9.1 PPC, NetBSD PPC, NetBSD 68k. The list is much longer than it was a few years ago.