Of course I'm not the only one to think of making a musical instrument/game.

fijuu

fijuu 1 was started around the same time as Shape Sequencer by two much more competent developers, and appeared at various high-profile international digital arts/media festivals. I found out about it about half-way through my first development phase and while finding it beautiful and exciting, hoped to make something a little less stylistically imposing on the player.

ergates

I found out about ergates when it was announced on the pd list last October and still haven't got it to run. I might investigate it again, now that bugfixes have been issued and pd HID support is getting attention from various angles.

More alternatives will be added as I remember/find them.