I discovered Project IceStorm while searching for FOSS FPGA toolchains. Clifford Wolf and Mathias Lasser worked to reverse-engineer the “iCE40” FPGA stick. The device itself is small, simple, and cheap, which made reverse-engineering it more feasible. Unfortunately, being a very tiny FPGA, there is not much room on the iCE40 to work with.

There are now a number of projects focused on extremely tiny Risc-V implementations, PicoRV32 being one of them (authored by the same Clifford as from IceStorm). I think PicoRV32 could be squeezed onto an iCE40. This would be extremely satisfying to me - a FOSS CPU flashed to an FPGA using FOSS tools.

According to January Risc-V workshop notes,

RV32M implemented in 2kLUTs at around 20MHz on the iCE40.