General information about Pixhawk designs, schematics, reference hardware, FMU versions, licensing, and trademarks, and contributing to the project can be found in the repo README.
FMUv3 was introduced in 2015. Identical to FMUv2, it doubled the usable flash to 2MB.
The FMUv3 design is used in the Pixhawk 2 FC board. This hardware is the result of a collaboration of the open hardware development community and 3D Robotics.
The design is provided in Altium Designer CAD files.
It consists of schematic files (*.SchDoc), BOM listings, and includes open reference hardware PCB layouts (.PrjPcb).
Tip PDF versions of the schematics and PCB layouts has been made available for easy previewing (i.e. if you don't have Altium Designer).