If we are talking about bit-serial CPUs, Olof Kindgren's SERV bears mention. It's a portable FPGA core rather than a breadboard, but it's bit-serial, RISC-V com

If we are talking about bit-serial CPUs, Olof Kindgren's SERV bears mention. It's a portable FPGA core rather than a breadboard, but it's bit-serial, RISC-V compliant and tiny!