NeXTStep (September 18, 1989) predates Linux (September 17, 1991)and it's window managers. I'd suggest you also look at Apple's work on ARM processors. They were first to 64 bit in that space.
”The company was founded in November 1990 as Advanced RISC Machines Ltd and structured as a joint venture between Acorn Computers, Apple Computer (now Apple Inc.) and VLSI Technology.”