Gil Weinberg and Scott Driscoll of Georgia Tech developed a robot that can improvise rhythms as it hears music:
Haile is a robotic percussionist that can listen to live players, analyze their music in real-time, and use the product of this analysis to play back in an improvisational manner. It is designed to combine the benefits of computational power and algorithmic music with the richness, visual interactivity, and expression of acoustic playing. We believe that when collaborating with live players, Haile can facilitate a musical experience that is not possible by any other means, inspiring players to interact with it in novel expressive manners, which leads to novel musical outcome.
http://www.cc.gatech.edu/~gilwein/Haile.htm via The Presurfer