Here’s an example of one of the many uses of NXT – PF cables (click here to see how to make them). It does most of its work mechanically, but its large PF motor is entirely NXT driven. This motor turns a small Lego rod and the wheel attached to it, which in turn holds 16 strings. These strings go through a specific hole in a circle (reversed Lego tracks), and through yet another, longer rod, after which they’re connected to the individual marbles.
It runs on motor port B, using the test program seen in the guide above.