The pi-topPROTO is a HAT-compatible add-on board for prototyping electronics for your pi-top or pi-topCEED. With plenty of space available to build circuits that can interact with your pi-top --- as well as a full 40-pin GPIO on top for a desired Raspberry Pi HAT --- the pi-topPROTO makes a great addition to the pi-top family.
To install, simply mount the pi-topPROTO to the modular rail inside of your pi-top and connect it via the 34-pin GPIO on the internal HUB Board, which can be daisy chained with other add-on boards.