get yourself a sonnet crescendo g3/g4 upgrade card, then you can run OSX (should you want to), MacOS, YDL, etc...
Well, that's good in theory, but in the US, they cost as much (or more) than a complete used G3 system. Plus they are slower, not officially supported for OSX 10.3, etc....
As it is, it'll run OS 8.5 and several flavors of Linux. I think mine has an old RedHat 6.2 PPC installed, though I also messed with YellowDog. Really, the box is quite useless. I haven't fired it up in over a year. I'd strip it and take the SCSI HD and CDROM out of it and chuck the rest, if it weren't serving the valuable purpose of keeping some old SGI IRIX installation notes from blowing away. ;-)