Yellowtail by Golan Levin

Yellowtail is an interactive software system for the gestural creation and performance of real-time abstract animation. Yellowtail repeats a user's strokes end-over-end, enabling simultaneous specification of a line's shape and quality of movement. Each line repeats according to its own period, producing an ever-changing and responsive display of lively, worm-like textures.
http://www.flong.com/projects/yellowtail/