For me, it's the Teensy 4.x boards. I have uses that consume all of their horsepower. I'm just a researcher, and my prototypes will be commercialized by an engineering team that will use the same microcontroller but on their own board and developed under their preferred auspices.

It's the closest I can get to an FPGA within my skill set.

Also, I think that Paul has been exemplary in his contributions to the open source community despite his own product having a closed component.