This game is basically a mix between a "easy to use game maker" a modding tool, a level editor and more stuff like that.Mario's Sandbox consists on some entities and tools for the blender game engine that generate a user-friendly game devolopment enviroment. Also this project aims to create a comunity where the users can create their own content and use content created by other users. So, let's just say that Mario's Sandbox is some kind of FPS maker and Pysics Sandbox
This it how it looks like when you are editing the game in the blender game engine for modding.