Interesting to think about a world where Apple was able to embed AIX with PPCToolbox running on the same machine with classic MacOS essentially as the window server. Assuming they could get around licensing cost issues, this might have been a viable path forward for a modern OS in an alternate future.
There was also Latitude porting toolkit, which was a sort of reverse engineered MacOS toolbox that mapped Macos calls to native Unix calls, including Rhapsody, at the source level. Adobe used it to port Illustrator and Photoshop to Solaris & Irix
