Well that's something I never expected to write. It turns out that Microsoft has open-sourced a small portion of their Edge web browser. This is the part that binds OpenGL ES 2.0 functionality, implemented atop Direct3D in Edge, to JavaScript for websites to directly interact with the user's GPU (as opposed to hardware-accelerated CSS effects for instance).

Websites can use WebGL to share 3D objects in an interactive way, have interesting backgrounds and decorations, or even render a video game.

This is not an open-source build of Microsoft Edge, though. It doesn't have the project files to actually be built into something useful. Microsoft intends for it to be reference, at least for now they say. If you are interested in using or contributing to this project for some reason, their GitHub readme file asks you to contact them. As for me? I just think it's neat.