I have owned two Elektron synthesizers, the Monomachine and the Analog Four, two very nice machines even though i have sold them both (mostly due to too many menus resulting in me not using them much). One feature i loved in particular was the arpeggiator that’s implemented in both synthesizers (and in their Octatrack as well). It has a built-in stepsequencer (of variable length) which allows you to skip certain steps in the ongoing arpeggio and to add note-offsets to certain steps, resulting in very interesting melodies and rhythms that are generated on the fly.
I decided to recreate that appreoach using Max For Live, which allows you to create custom audio/midi devices for Ableton Live with Max/MSP. A very first alpha-release of the so-called Arpektron can be found here, and you can listen to a demonstration of the device controlling my MS-20 Mini on SoundCloud.