Raspberry Pi is broadly used for IoT, and there is a lot of software for it. But I would like to know about any completely open source designs, including software and hardware (PCB, not components).
I have heard about Banana Pi but I'm not sure if it's completely open source or if other alternatives exist.
The main requirement is to be fully compatible with any of the broadly existing software platforms (Arduino, Raspberry Pi).
Of course, the components used in PCB should be available to anyone.