Questions.

What is this about?

This is PrBoom ported to browser! Here is the GitHub if you want to try: https://github.com/UstymUkhman/webDOOM

Isn't this piracy?

Well yes. Kind of. This is shareware version of Doom. Meaning you can only play first episode. The rest? Buy it.

Doom 2?

I am not sure. Doom 2 doesn't have shareware version. Meaning you can play entire of doom 2. Bethesda might not like it.

How was this created?

It was created by the power of webassembly and using emscripten!