Tynker - Game Worlds for Kids to Learn Programming
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
CodeCombat - Learn programming with a multiplayer live coding strategy game.
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
StackHive - Design, develop or publish websites right from your browser
WaveEngine - The definitive free cross-platform mobile engine to unleash your games using C#.