Originally Posted by DrBong
How about BeOS then (or Haiku as the open source version is known now)?
If it isn't too heavy for 68K (perhaps a lite version if it is?), then there would be a reasonable foundation of software ready to use if someone managed an optimised port to Amiga. Also, it's probably one of the most clean Amiga-like operating systems that has been developed since AmigaOS.
That's worth taking a look at.