Arcade controls posted this new project.

Added dualstik - arcade controller with spinner and trackball for two players to the example page.

The author had this to say about their project:

The dualstik consists of two controllers linked together with a 25 pin serial cable.
The master unit provides buttons, a spinner and a trackball, and can be solitary used in single player games.
The slave controller looks similar, but it only works when connected to the master, because it just holds the controls for player two and doesn't contain any logic boards. This provides for a handy size of the single unit while the duel player option is still retained.

Source .