When you say preset sequences do you mean that you want to be able to create sequences and then recall them or play through them randomly? Or that you want the sequencer to have pre-set sequences already loaded?
One thing to consider is creating a series of midi clips in Live and then working with the “next clip” (not sure what real name for this is) settings to control randomization between which clips are loaded. That way you can create phrases of arbitrary lengths and see how they recombine.
You can then play through those and record them in timeline view and chop and edit the good ones at will.
Rozeta is a solid recommendation. I’d also take a look at Fugue Machine. Conceptually it’s a bit different since it’s as much a multi-playhead tape machine as it is a sequencer. But it satisfies all your other requirements and is immensely fun to work within.
Sounds like the sequencer I made for Norns, largely inspired by the Elektron sequencer and the Endless sequencer of an OP-1. Randomization everywhere, but it became so complicated and very hard to document that I never released it (It’s still a wip though)
That being said, if it’s supposed to be custom and powerful, what about a Max standalone and/or M4l device ? You could use the Live step sequencer as a starting block (randomization is built in) or perhaps start something new and work with a Dictionary + a JS object and a multi-slider object
Wow - Not being familiar, I downloaded it tonight. I love it!! Thank you for mention, @bran — I love that each of the four separate channels play at different speed and separate midi channel too. Seems from the same maker as the Arpeggionome, which I’ve used for years. Fugue looks intense and is immediately very beautiful sounding. Looking forward to connecting to other equipment with it.