microStudio - microStudio is an all-in-one online game engine that enables you to create games, develop programming skills, have fun playing what you have created, share with others, and prototype.
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Open 3D Engine - Open 3D Engine is an open-source 3D game development engine in real-time.
ENIGMA – LateralGM - LateralGM is a powerful IDE for ENIGMA, and both of these combine to offer you a cross-platform game environment.
WaveEngine - The definitive free cross-platform mobile engine to unleash your games using C#.