Topic: General Purpose Breakout Board + FPGA interface user guide

We've got a user guide for the GPBB up on our wiki:

The GPBB is the starting point for most hardware hacks, as it brings out several FPGA-based I/Os and includes some analog interface capabilities.

If you want to design your own FPGA modules, even if they don't involve external hardware, it's recommended you look at this guide and snag the interface modules as a starting point for your design.