1.torvalds / linuxLinux kernel source treeCOther license254K total67K forks+3,902 starsfrom 250,391 · score 8.27
2.reactos / reactosA free Windows-compatible Operating Systemoperating-systemckernelososdevx86+7 moreCGPL-2.018K total2.3K forks+295 starsfrom 18,132 · score 5.69
3.mit-pdos / xv6-riscvXv6 for RISC-VCOther license11K total4.6K forks+177 starsfrom 10,566 · score 5.18