Here is a Tabby installer USB image!
If you want to try this, you probably need to use Open Firmware to get your Mac to boot the USB. I’ve tested it most on an aluminum PowerBook G4, but this will likely work(ish) on many more Macs.
WARNING: this is extremely experimental software. Your already crumbling Power Mac might literally explode (laughs in PMU). Use on your fragile 25-year-old PPC Macs at your own risk.