This demonstration should give you an idea...
Yes, it's a hardware interface add-on for the Raspberry Pi. It reminds me so much of the sort of thing my brother and I (mostly him) built ourselves, back in the early 'eighties at the family home in Morden. The row of LEDs and the momentary-contact pushbuttons are so reminiscent of a very basic computer (with 1 kiloByte of memory!) built into a silver-and-green casing that I had, with a Motorola 6800 CPU at its heart.
Ah, those were the days! The memories the GertBoard thus brought back to me were quite powerful, and reminded me of just how much I still had to learn in those times.
Anyway, we are now some thirty years on, and still the spirit of "breadboard innovation" and experimentation lives on. It really is important for the future, to help prevent stagnation in some of the fields in which the technology can continue to flourish and develop.