A couple of years ago I saw an artist at a music festival using a piece of software to create a loop/sample/synth piece of music. The software had a black and white user interface, with blocks representing different loops. One of the distinctive characteristics of the interface was that each block had a progress bar that moved across the block as the loop played back, and it appeared to me that the blocks had different lengths, and could be synchronous or asynchronous.
What was that piece of software?