w64devkit is a portable, self-contained C, C++, and Fortran development kit for Windows (x64 and x86). It is built entirely from source using a Docker-based multi-stage build system, producing a signed self-extracting 7z archive that requires no installation and runs as any user. The kit includes Mingw-w64 GCC, GDB, GNU Make, CMake, Ninja, BusyBox-w32, Vim, Ctags, Ccache, NSIS, 7-Zip, and a collection of custom utilities (debugbreak, recycle, uuidgen, peports, pkg-config, rexxd, vc++filt, w64devkit launcher). All custom utilities are compiled as tiny, CRT-free executables using -nostartfiles and -nostdlib, linking only kernel32 and custom libraries. The build process applies a curated set of quilt patches to upstream sources to improve Windows compatibility, cross-compilation, and console handling. The repository also includes a full reimplementation of the quilt patch management tool in C++20 (src/quilt.cpp) with built-in diff and patch engines. The codebase demonstrates high craftsmanship in low-level Windows programming, with careful attention to performance (SWAR optimizations, inline assembly), correctness (handling of link.exe bugs, edge cases), and minimal dependencies.