PG Music's Band-in-a-Box still exists, but way back in the Windows 3.1 era it already had a "snap to pleasant notes" feature if you wanted to play along a set of chords on a MIDI piano. It could also play chords in the style of famous musicians along with your never-ever-bad notes! I always switched it to the "Erroll Garner" preset and hammered away.

https://en.wikipedia.org/wiki/Band-in-a-Box