I think it's the open source code spun off of Docker to clearly set it apart from Docker the company. They call it building blocks for containerization projects (probably mostly Docker itself). I remember at the time it being a confusion: did Docker get renamed? (It wasn't.) To me the real question is, what's prompting this to appear on the main page again now?

I use it for running containers on Windows, that's the only reason I even come close to it :/