I was actually thinking in the Setun: https://en.wikipedia.org/wiki/Setun and DSSP. But thanks for the reference, I did not know Malbolge (though it looks like it uses the set 0, 1, 2 instead of the IMO more useful -1, 0, 1).
Malbolge (and Dis) are the classic ternary esolangs. I fiddled around with that in a long lost esolang back in the day.
Keep in mind that Malbolge is meant to be awkward, so while (-1, 0, 1) might be more useful, (0, 1, 2) suit Malbolge's perverseness much better, though I doubt that was a conscious decision.
This is when you know you're about to experience a steep, learning curve:
"language designed to be as difficult to program in as possible. The first "Hello, world!" program written in it was produced by a Lisp program using a local beam search of the space of all possible programs."
