Loopo is a sampler with a very simple twist: it does not start playing a sample at the start, but in the middle. If your source material rhythmically matches, then everything you play will be in rhythm, no matter how you play.

One way to think about is that all your loops are playing at the same time, but are muted. A MIDI note-on unmutes the loop, and a note-off re-mutes it.

Loopo was built with Juce and works in most mainstream digital audio workstations.