Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Blitz3D - Create 2D and 3D Games for Windows.
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
BlitzPlus - Create 2D Games for Windows.
WaveEngine - The definitive free cross-platform mobile engine to unleash your games using C#.
Monkey 2 - An easy to use, cross platform, games oriented programming language