Its a general purpose 72 pin backplane for either card edge connectors or pin headers.
It can be stacked in a longer backplane via angled pin headers on both ends.

Pin 1 is power, connected to thick power trace on top layer.
Pin 2 is ground, groundplane is the entire bottom layer.

Its the cheapest generic backplane I could come up with that makes modular projects much easier.
I needed this for some upcoming projects.