Alias renders all of its own UI in OpenGL, so in theory, it was as simple as “Get a GLContext, and render to that”. Porting to Mac OS occurred in 2008 (I think) and was a reasonably sized project. It was a little janky to use as a modeller 8 hours a day, but good enough for a development workflow. This was a fantastic strategic decision because it allowed Studio to port to various flavours of Irix, HP Unix, Windows, Mac OS, and even Linux. That meant that Alias could run on any OS that supported OpenGL. OpenGL formalized in the early 90s and Alias (the company) ported Studio to support this nascent API. Back then, the company was Alias (merged with Wavefront and ultimately acquired by Autodesk in 2006) and the software was called Studio. Alias development started back in the late 80s and was written for (I think) SGI machines. I was part of the team that ported Alias to MacOS. ` I worked at Autodesk from 2007 - 2011 and on Alias / Alias-related things for a good chunk of that.

Some more information from an (apparent) insider why Autodesk took the decision to stop supporting the upcoming MacOS version with Alias & VRED.

Mac os opengl support