Neo6502 - Open Source Hardware Board
6502-based sbc with a "rp2040 soc" (i.e., the rp2040 implements all of the peripherals)
Pico as Z80 RAM & RAM: Homebrew Retro Computer Part 2 – Maker Hacks
with just a little bit of micropython code. neat!
MicroMac, a Macintosh for under £5
relating a fun adventure: emulating a 128k mac on a pi pico