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!
Godot Engine - Feature-packed 2D and 3D open source game engine.
MonoGame - MonoGame is an open source implementation of the Microsoft XNA 4 Framework.
RPG Paper Maker - Website
ct.js - ct.js is a 2D game editor (desktop app) based on web technologies.
Solarus Action-RPG game engine - Solarus is a free and open-source Action-RPG game engine.