QEMU
I've heard of the QEMU classic machine emulator. I've found this link
http://wiki.qemu.org/Main_Page
but does someone know of a link that talks a little more about emulating a ppc?
R
Mac mini, OS X Yosemite (10.10.5), Fall 2014; iPhone 4 7.1.2
Sheepshaver if you're interested in early OS9.
Running Snow Leopard server with Rosetta in a virtual environment. Here's an old article and I am sure you can find newer though it is likely to be similar. Installing Snow Leopard (and Rosetta) into Parallels 7 in Lion - http://forums.macrumors.com/showthread.php?t=1365439