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.
Snap - Snap (formerly BYOB) is a visual, drag-and-drop programming language.
Cyberix3D - Free online 3D Game Maker. Make your own 3D games online!
Blockly - Blockly is a library for building visual programming editors.
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.