[dvdbloc]

The ARM Cortex-M7 architecture is not open, not sure if that’s what the OP was referring to. RISC-V would be an example of an open architecture.

[fermienrico]

That's true, at some point in the abstraction layers from Teensy to the silicon atoms, the concept of "open-source" disintegrates. But to clarify, I am mainly concerned with the top layer - gerber files, schematics, bootloader, etc.