You may have seen or heard of Matt Mower's Elysium, which will soon go into public beta. (Like maybe tomorrow.) Lucky me, I'm in on the private beta (woo woo etc.) and got it driving my Korg hardware today.
The second mp3 uses probabilistic features in Elysium, kind of like Archaeopteryx. Where Archaeopteryx gives you a probability matrix step sequencer, Elysium gives you a hexagonal programmatic step sequencer with probabilistic and mathematical features. To unravel that, let's start with the hexagons.
Elysium's kind of like a software version of the reacTogon:
Elysium replicates this interface in software, swapping out the built-in synth for external MIDI control, and adding in some new features. One of these is that individual notes can have arbitrarily complex callback functions in MacRuby.
Another is that you can assign a probability to each note, expressing as a percentage how likely it is to play on any given iteration of the sequence. You can also attach oscillators to any note, which vary parameters such as note volume and length on a regular or irregular rhythm.
To put this in context, consider the guitar riff from "Money For Nothing" by Dire Straits.
As a kid, I once destroyed my dad's stereo with this song. Luckily he wasn't home and I blamed it on the dog. Yes - the dog. I know it seems unlikely that a dog would turn on the stereo, but our dog was part wolf and incredibly destructive. I could blame almost anything on him. Anyway, I tried to get my guitar teacher to teach me this, but he said I wasn't ready; apparently Mark Knopfler plays the riff a little differently almost every time through. I'm not even sure that's true, but if you want to make a riff on a synth for which it is true, Elysium's a very appropriate tool.
It's true of my probabilistic riff mp3, for example - the riff never repeats exactly the same way - and that only takes advantage of the probability settings. I played with the oscillators as well and there's a lot of power there for expressive texture and subtle nuance. I haven't even gotten to the embedded scripting yet.
Update: Elysium is now in public beta. Here's a better example of a probabilistic riff, with a regular, non-probabilistic drum beat. Here's video where I record the riff in Elysium, without the beat, but with some Elysium-driven drums.