Funnily enough I was playing with a couple of old PowerMac G4s a couple of weeks ago (actually wiping them for disposal - though I've since decided to keep at least one!)

I realised very quickly that I'd forgotten how good the OS9 interface is, and how well it stands up against today's offerings. Trying out a lookalike theme on Linux [1] is definitely on my todo list:

[1] https://github.com/grassmunk/Platinum9