Contemporary Mac OS X has more in common with NeXTSTEP than with classic Mac OS. When it was obvious that classic Mac OS design has limitation which cannot be overcome, and after several failed internal replacement projects at Apple (including the infamous Copland), the company started looking outside. When it was almost certain that BeOS will serve as a framework for the new OS, Apple surprised everyone by buying out NeXT, Inc., and using their operating system. BeOS was allegedly too limited (it couldn’t even print!) and too expensive. OS/2 and Windows NT were also considered alternatives, as both had PowerPC versions at the time.
The interesting terminology of Apple Lisa seems to have inspired other GUI architects. Authors of OS/2 2.0 Workplace Shell wrote in their guidelines “We characterize the Minimize and Hide actions as requests to ‘put aside temporarily,’ while Close is thought of as ‘put away.’” This is almost identical to “Set Aside” and “Put Away” options of Lisa.
To prototype and test a Workspace Shell GUI for OS/2 2.0, IBM used the legendary, heavily object-oriented SmallTalk V/PM.