Re: I wish the Pi universe was a bit more cooperative and played well with others.
1. We've been putting a lot of effort (and money) in to upstreaming as much as we can. Hence we now have open source graphics (DRM, Mesa etc), a standard camera interface, libcamera, and now use V4L2 rather than openMax to get access to the codecs etc. There is some stuff that would never be accepted upstream though.
2. HAT's are a Raspberry Pi design/invention, I guess if other people want to use them, then they simply have to adhere to the spec?
3. What wrong with Raspberry Pi OS?
I agree with the comments about SBCs from China and Armbian. They are certainly not a panacea.
Biting the hand that feeds IT
