GeeXLab - GeeXLab - cross-platform tool for game development, 3D programming, creative coding and prototyping
Godot Engine - Feature-packed 2D and 3D open source game engine.
LOVE 2D - Hi there! LÖVE is an *awesome* framework you can use to make 2D games in Lua.
Unity - The multiplatform game creation tools for everyone.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.