Too bad the WSL (Windows Subsystem for Linux) is not open source. It is already an impressive piece of software, but many features are still lacking (e.g., neither Valgrind nor gperftools work right now), and it could benefit greatly from community involvement.
Fittingly, issue #1 in the WSL bug tracker is requesting it to be open-sourced: https://github.com/Microsoft/BashOnWindows/issues/1