There were a few nubus clones. I had a Radius 81/110 with a nubus-based board.
Check your specs and system profiler if its still got the macos on it. If its PCI any recent release should be able to run on it (maybe not bootable from the CD in all cases). With a nubus model your best bet is with MkLinux which is an older redhat-based version (v.5 I believe), and there are kernel replacements that will let you run yellowdog and some of the other variants.
MkLinux is found here (for nubus) with the PR1 release the most current:
http://www.mklinux.org/
YellowDog can be downloaded from here:
http://www.yellowdoglinux.com/
Look at sourceforge for newer kernels that will allow nubus machines to run newer linux variants:
http://nubus-pmac.sourceforge.net/
If you haven't done an install of linux before the older machines are not as straightforward as the new world machines. Read the instructions very carefully and follow them precisely. Good luck and post if you have any trouble.