Principia is a physics-based sandbox game that includes electronics, circuiting, robotics, Lua scripting capabilities, cute little robots you can control or fight against, and more.
There are about 29 000 levels (including the amount available in the level archive) that are everything from controllable vehicles and other contraptions to minigames, robot adventures, pixel art, or something completely out there.
The game started out as a paid mobile game in 2013 and was later available for Windows in 2014, but ended up being abandoned due to financial issues. Recently it was finally released as an open source project and is now completely free. I have become the maintainer of the open source project and I also host the new community site for the game (which started out as an unofficial replacement when the official was shut down), so I presume this counts as a "Show HN".
Be sure to check it out! :)