Pretty sure MultiTOS (which was derived from MiNT IIRC) fully supported preemptive multitasking back in 1992 or so when it came out. This, plus the fancier graphics support, a proper 68030 instead of the rather cut down 68EC020, and addition of a Motorola 56K DSP, meant the Atari Falcon was superior to the Amiga A1200, at least on paper. I certainly adored mine when I owned it not that long ago as a part of my small collection.