RPG Maker - Make your own PC game with RPG Maker. Our easy to use tools are simple enough for a child, and powerful enough for a developer. Try it free today!
Unity - The multiplatform game creation tools for everyone.
Godot Engine - Feature-packed 2D and 3D open source game engine.
RPG Paper Maker - Website
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Solarus Action-RPG game engine - Solarus is a free and open-source Action-RPG game engine.