I am currently using my Catweasel MK4 in my PowerMac G4 computer.
The card is not compatible with the PowerMac G5 computers. The G5 does not provide the 5 volt power and signaling the card requires. It turns out the previous statement isn’t true. There are three types of PowerMac G5s: PCI, PCI-X and PCI Express. I just tested a Catweasel MK4 card in a PowerMac G5 PCI-X machine and the floppy I/O functions worked just fine. I did not test the SIDs or the keyboard/joystick functions.
The Catweasel MK4 is not a PCI Express card. So it work work in late model PowerMac G5s or any Mac Pro.