Teensy's closed bootloader, USB stack, hardware design are what is proprietary. But the toolchain is open. Eg: I can use PlatformIO, etc. From my perspective an open alternative would splinter the community rather than replace it. Developers value Teensy's polish & consistency (PAnd this is Paul Stoffregen's discipline). If you endeavor to follow this path, you'd see adoption from transparency advocates and research/security-focused devs, but pragmatists like myself would stick with what works and what's affordable. Your real problem is replicating that engineering rigor in an open-source project, is a lot harder than it looks. Let me give an example; STM32 is more open but shows us exactly what fragmentation looks like without unified vision.