GEM and GEMDOS, which are perhaps best known from the Atari ST series, were also ported to the Lisa. Both were designed to be portable, and DRI sent the source for the Lisa port to OEMs that were considering porting GEM as their 'example implementation'. When Caldera/SCO open sourced GEM, part of the random dump of stuff they threw at the folks requesting it was this porting kit. The FreeGEM folks were mostly interested in PC GEM (I was on the periphery of this, fiddling with programming language bindings), and Atari GEM had gone its own way anyway. Bits of it did end up in EmuTOS, though.