[sudobash1]

It is linked at the top of the article. It is a physics-based sandbox building game. Back in the day it was commercial, but it was abandoned a while back and somewhat more recently released as open-source.

[LorenDB]

It's also the name of an n-body physics mod for Kerbal Space Program.

https://github.com/mockingbirdnest/Principia

[shellwizard]

Is it like Garry's mod?