The Reactogon chain reactive performance arpeggiator is a unique musical synthesizer that uses small tokens placed on a hexagonal board to create music.
The tokens have different characteristics; some provide more than one direction for the arpeggianation (if that's a word) to proceed. Others provide stops. Musical sequences can be created using artfully placed disks. Take a look at (and a listen to) the Reactogon video below.
The Reactogon synthesizer reminded me of another tabletop music inteface. Reactable is a multi-user electro-acoustic music synthesizer with a unique tabletop interface. Performers (like maybe you) control the instrument by placing objects on the table and moving them around. Check out the demo below, and turn your sound up a little.
I love science fiction instruments; take a look at the Smule ocarina, which you can download on your iPhone. See also the literary instruments like stimic from Jack Vance's classic 1976 story The Moon Moth and the incredible Krang from Alan Dean Foster's 1972 novel The Tar-Aiym Krang.