I like making generative music - writing rules & procedures to determine musical elements, instead of writing them explicitly - in Ableton Live, a powerful and creative digital audio workstation.
In Ableton Live, I can use "MIDI Devices" to modify a static, one-note input MIDI signal into melodies, rhythmic patterns, chords, arpeggios, and more. These MIDI devices control musical elements like pitch, rhythm, scale, velocity, note length, delay, and chance, with a musician-friendly UI more similar to a physical effects pedal than a scripting terminal.
Check out the generative music I make at masonlynass.bandcamp.com