This is the Wii Nunchuck female PCB connector. It lets you use the Wii Nunchuck in your designs, which opens up lots of interesting possibilities for control: Nunchucks are available for like $5 on ebay, have a well-documented protocol, and include a 3 axis accelerometer, X-Y joystick and two buttons.

People have been using Wii Nunchucks to control their own electronics for several years now, but few have had the real connector. Most have simply printed contacts on to a PCB and stuck the PCB in to the nunchuck, but this method has poor retention. The real connector can hold on to the retention tabs of the Nunchuck, letting you flail around with confidence!

These are left over from a failed project we had. They were kind of a pain to get from China, and we've got a fair amount left over.