(There's no video for Ubuntu 6.06 for PowerPC (G3, G4, G5) yet. Please contribute to MR and add a video now!)
This is Ubuntu 6 for your PowerPC Mac.
(672.64 MiB / 705.32 MB)
Ubuntu 6.06.1 (Dapper Drake) for PowerPC Macs / ISO image, zipped
For Apple Macintosh G3, G4, and G5 computers, including iBooks and PowerBooks as well as IBM OpenPower machines.
At least 256MB of RAM
Emulating this? It could probably run under: QEMU