This unfortunately named product is actually the PPC platform's equivilent of VMWare. It allows you to run the Mac OS within a safe little hardware abstraction bubble that runs on top of linux. Thus it provides the handy feature of being able to run the Mac OS side by side with Linux on the same box at the same time, meaning you can use Linux for your sysadmin-like tasks, drop into Mac-on-linux for those two or three mac apps you just have to use, and still have your linux kernel, with its memory protection and all, still functional after the Mac OS inevitably crashes.

Mac-on-linux was created by some swedish company called Ibrium HB. However it is fully open-source and free and GPLed, and can be found bundled with most PPC linux distributions (LinuxPPC and Yellow Dog Linux i know of). In this respect it is maybe a tiny bit closer to a less abstract version of Plex86 (FreeMWare) than to VMWare.

Hardware abstraction is not emulation!