An interesting software for a historic view is Rhapsody DR 2,its a mix of Code fromOS 8.5, Openstep 4.2,and mac OS X Server 1.x and a bit of Copland.
Cocoa is called "yellow box" and that what became classic env is called "blue box" and runs a full OS 8.5.
DR2 is available for X86 (P I+) and PPC (603e+ PCI).
Rhapsody is incompatible with OS X UFS filesystems and darwin,OS X , Openstep apps and drivers.
OS X DP 2 looked like Rhapsody but had the XNU kernel + IOkit + cocoa.