Vox-L is one of the games that we're producing at ThoughtSTEM. How to describe Vox-L... think about it like this: It's what would happen if Gary's Mod and Minecraft had a secret love-child. You can find the project site here: vox-l.com.
Vox-L is somewhere between a game and a game engine, so we call it an "engine game".
Vox-L started as an emulator for Minecraft modding in LearnToMod -- one of ThoughtSTEM's other projects. Since then, Vox-L has become more extensible than just an emulator, with added support for physics, custom assets, and an event-driven modding API.
Physics video demo: