powdertoy.co.uk
The Powder Toy is a free open-source desktop falling sand physics sandbox game. It simulates air pressure, velocity, heat, gravity, and interactions between various substances, providing building materials, liquids, gases, and electronic components for users to construct machines, terrains, or other creations. Users can browse and upload community saves, and the game includes a Lua API for automation and plugin development. Its source code is distributed under the GNU General Public License.