AROS is a 100% 3.1 API compatible Amiga Workbench which portable to different platforms, such as x86, PPC and even 68k. It was a project started back when Commodore folded and when the future seemed non existent for AmigaOS.
AROS lacks support for running native 68k Amiga programs, something that an integrated UAE is going to solve, so that you should be able to run 68k programs in AROS just as if the program was an AROS program.