If you just need a PPC MacOSX emulator, look at PearPC. My laptop couldn't emulate a G3 at full speed in 2004 when I first tried it, but I'll bet a modern CPU would have a better chance.

This project doesn't look like it's emulating PowerPC, though. It's tracing the binary, disassembling it, and generating equivalent C++ code. It's a technique called static recompilation.