SooperLooper is a live looping sampler capable of immediate loop recording, overdubbing, multiplying, reversing and more. It allows for multiple simultaneous multi-channel loops limited only by your computer's available memory.
The application is a standalone JACK client with an engine controllable via OSC and MIDI. It also includes a GUI which communicates with the engine via OSC (even over a network) for user-friendly control on a desktop. However, this kind of live performance looping tool is most effectively used via hardware (midi footpedals, etc) and the engine can be run standalone on a computer without a monitor.