Scratch - Scratch is the programming language & online community where young people create stories, games, & animations.
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Tynker - Game Worlds for Kids to Learn Programming
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
RoboGarden - RoboGarden provides a complete, game-based suite that teaches coding from beginner to professional level, starting with block programming and progressing to professional Python and JavaScript programming.
WaveEngine - The definitive free cross-platform mobile engine to unleash your games using C#.