Well, AmigaOS was released on the Amiga 1000 in 1985. A fully preemptive multitasking OS with a mouse/windowing GUI. Being able to display 4096 colors on screen with graphics, audio, and IO coprocessors made it a giant leap at the time. Was never huge in the States though.
Thought to be a game machine by USA shoppers. But could do anything if programmed. Like word processing, or desktop video, or desktop publishing. The preemptive multitasking, 8 bit stereo sound(good for the time), up to 8 different whole screens displayed (not just a window) at different resolutions, co-processing chips(sound/graphics) and NTSC video output was very advanced for the time for a home computer for 1985.
The stuff that sold pc was off the shelf components, and free OS. (Ms-Dos), and early business programs (visi-calc),...Apple was very user friendly, nice graphics (2 color) and comparatively elegant compared to the PC but tooooo propietary IMHO