Microsoft's Windows Subsystem for Linux, or WSL, is a compatibility layer that allows people to run Linux distributions directly on their Windows machines, foregoing the need to configure a virtual machine or dual-boot setup.
Microsoft surprised us with this one.
Open sourced under the MIT License, WSL is now fully available for anyone to inspect, modify, and contribute to, with its very first GitHub issue, opened back in April 2016, now finally closed nine years later.
Microsoft says that it open sourced WSL to encourage community contributions and accelerate its development while improving Linux support on Windows.