The Alpha Syntauri was a music system designed around the Apple II, 20 years before soft synths came to the scene. It features 16 digital oscillators, 8-note stereo polyphony and 8-part multi-timbrality - with an external keyboard available in 49 or 61 key versions (the latter of which was velocity-sensitive).
In this video Ellen Lapham, the then president of Syntauri Corportation goes over the system described by Vintage Synth Explorer as sounding "fiercely, aggressively digital". Alongside her is the father of FM, John Chowning who shows some of his synthesis experiments with the machine.
It's a great demo if you can handle the reasonably low-fidelity upload. There are some more intriguing music video from the same channel: https://www.youtube.com/c/mekonin/videos
Angry little feller
Matths gives it a workout
From recent Brighton gig
With Matt Hodson