Commodore Amiga
the Commodore Amiga Computer.
not so big in music and composing but very big for most of us using Trackers, that are 4 voice sound tools based on sequencing on a more machine-code like way of composing as the nanoloop does today (roughly said).
Dr.T's KCS and Bars & Pipes where possibly the only Pro Sequencers on the Amiga but there were quite a lot of Trackers that where able to use the new sampling technology, the Amiga offered or even Synthesis (but much less used on those tracks).
it was also based on the Motorola 16 Bit Processor 68000 but slightly below 8 Mhz compared to the Atari ST, but it's success came mainly because it had better graphics, better built in sound (aim: for games) and it had a cool multi-tasking OS but that wasn't a real reason those days.