All is not lost if you want a Unix-like system.  
Try these links:

http://www.macbsd.com/openmac/index.html
http://www2.giganet.net/~mark/NetBSD/
http://www.openbsd.org/mac68k.html
http://maclinux.wwaves.com/

And, the only permutation left: let's say you have 
Unix, but you want Mac:  well, for a free solution 
try:

http://www.leb.net/vmac/
http://www.tcs.auckland.ac.nz/~edouard/MkLinux/vmac.html

http://www.mac.linux-m68k.org/