Godot Engine - Feature-packed 2D and 3D open source game engine.
Machinarium - Machinarium is independent puzzle / adventure game by Amanita Design
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
Unmechanical - Fun and atmospheric side-scrolling puzzle adventure.
Unreal Engine - Unreal Engine 4 is a suite of integrated tools for game developers to design and build games, simulations, and visualizations.
Limbo - “Dark, disturbing, yet eerily beautiful, Limbo is a world that deserves to be explored.” Joystiq. “Limbo is as close to perfect at what it does as a game can get.” Destructoid. Buy LIMBO: Special Edition.