A modified version of the Second Life viewer that allows;
- connecting a serial device to the viewer
- controlling movement of the avatar according to GPS readings
- controlling the camera according to accelerometer & magnetometer readings
The combination of these features allows you to do things like connect an accelerometer, magnetometer & GPS receiver to an Arduino, have it dump readings into the viewer & have the viewer use them to control the avatar & camera.
More information about this project, including build instructions, is available in this blog post.