MIDI Navigator, below, is a Mac OS X MIDI driver for the 3dconnexion Space Navigator, right.

Usage is simple: download the application, launch it and select SpaceNavigator in your favorite MIDI application as input device.

MIDI Navigator can send relative and absolute CC commands. You can adjust the CC number, mode and sensitivity for each of the six degrees of freedom.

Rui Gato has created a demo video of this in action.

Requires Mac OS X 10.4 and a 3dconnexion Space Navigator.