I held a guest lecture at the speech, music and hearing group at KTH in Stockholm a couple of weeks ago, and got a tour of the lab afterwards. There I got a demonstration of the Optitrack optical motion capture system, which, as compared to other similar systems, is an amazingly cheap solution starting at $4999. Obviously, it has lower accuracy and precision than the larger systems, but then it also costs 1/20 of the price… However, 100 Hz speed and millimeter precision is decent for a USB-based system, and the cameras are really portable (10×5 cm or so each). The best thing was that the KTH people had written a small program sending OSC in realtime, and they showed a demo where the system would control a PD patch on another computer.