I've actually thought about creating something like this. It looks pretty good for combating RSI. Because it would allow you to have your arms in any position.

I've actually thought about creating something like this. It looks pretty good for combating RSI. Because it would allow you to have your arms in any position. However, I think it would be necessary to have two of them, one in each hand. And maybe a small trackball on one of them. It would probably also help to have straps on them that wrap around your hand, so you didn't need to grip them to keep them from falling to the floor.