Platinum Arts Sandbox Free 3D Game Maker is an open source game design program for kids and adults based on the Cube 2 Engine. Through the ingame and cooperative editing and focus on ease of use the program is easy enough for kids to use but powerful enough for full game projects. Sandbox includes Save The Princess Gameplay, an RPG Maker, a Sidescoller maker, a Movie Maker aka Machinima, Save The Banana Base Capture, and more! Sandbox is already being used in many schools and colleges throughout the world and included in game design contests.
This is my favorite engine.
Everything is easy to learn and understand, but it's still powerful.
The community is very helpful and it's actively developed.
You can create a variety of games with this.
Mapmodels decrease performance too much.
The Game Design Community/Social Site is not really used.
But overall a very good engine, so I give it 10/10 points.
Sandbox is a free game maker/engine and the only game maker/engine of what i know off which has a in-game editor, might not have the best graphics in the world but it is still great, if you want to make a small game or a large game this is the game maker/engine for you.