commons/raspberry-pi-pico
RP2040 with dual Cortex-M0+, 264 KB SRAM and the PIO state machines that make it worth forking.
RP2040: two Cortex-M0+ cores at 133 MHz, 264 KB of SRAM, and no internal flash — code runs from an external QSPI part.
PIO
The reason to build on this rather than any other cheap MCU. Eight programmable I/O state machines let you bit-bang protocols the silicon has no peripheral for — DVI, WS2812, quadrature encoders — without burning CPU time.
Castellated edges mean the whole board can be reflowed onto a carrier as a module.