The diodes are to drop the 5V DC power brick output down to around 3V for input to the FPGA power supply (1.2 and 2.5V LDO regulators in the foreground), just to keep the regulator chip temperatures down (its also why the board is mounted vertically, improves air flow). Since the contraption is currently in my bedroom, I'm using passive cooling as the fans were keeping me awake.

Most of the hi-tech is inside the FPGA chips, the breadboard is really just used as a patch panel. The only active components are a 74HC244 buffer for the byteblaster-clone that programs the FPGA's (driven bit-bang style from the raspberry pi gpio's), a couple of opto-isolators for the serial comms (again to the raspi, but passing through a DE0-Nano for obscure historical reasons), a 20MHz oscillator module (attached dead-bug style since its a SMT part) and a smattering of transistors/leds for monitoring.

I always enjoyed the Heath Robinson style cartoons as a kid, seems to have rubbed off on me somewhat