I know this was in jest, but had some of Apple’s and IBM’s 1990s plans came to fruition, we could’ve ended up with an operating system capable of running both OS/2 and Taligent (the original planned successor to the classic Mac OS) applications on PowerPC hardware (one of the few parts of the Apple/IBM collaboration that was realized):

https://en.wikipedia.org/wiki/Workplace_OS

OS/X Warp sounds a lot cooler than Workplace OS.