Lightly used Korg SQ-1. This is an analog sequencer for use with other synthesizers or a modular rack system.
Accepts USB power and a variety of inputs (CV & Sync, etc).
Outputs both CV and MIDI, which makes this an extremely versatile little box. I've used it to sequence discrete digital and analog synths and as a master clock.
Variety of sequencer settings to improvise sequences across various scales. The interface is extremely easy, it's very WYSIWYG, every I/O and option is visible here except the power supply on the opposite face.