[tamlin]

There was a Linux subsystem for NT around early 2000s in Microsoft Research.

There is amazing depth inside parts of Microsoft. For example, a team built Xbox360-on-PC sometime around 2007-08. That was emulating the PowerPC and GPU on Intel PCs. This didn't ship for various reasons as a product, but it was in the draw when Xbox One came along and they wanted game compatibility between Xbox 360 and XBox One.

WSLv1 was built on Drawbridge that originally came from MSR. I heard a rumor that WSL was spun out from a project using Drawbridge to run Android. Obviously a lot of work went into WSL subsequently, but the pieces to get started were in place.