A teaching operating system (2K LOC) on QEMU and RISC-V boards
The open-source RISC-V core that you can shape to your needs! (Verilog code generator)
A FPGA friendly 32 bit RISC-V CPU implementation
https://github.com/SpinalHDL/VexRiscv
The RISC-V Virtual Machine
https://github.com/LekKit/RVVM
https://www.youtube.com/watch?v=t5q0M5VDlQM
https://www.linkedin.com/pulse/how-build-risc-v-cpu-custom-instructions-steve-hoover-g4jjc/