A GDG file is a project file used by GDevelop, an open source program used to create games without programming knowledge. It contains information about a game such as events, objects, and scenes. The file allows you to save and resume your progress when developing a game.
The GDevelop application is designed for all types of users that want to create a 2D game without extensive programming knowledge. You can illustrate scenes, add and animate objects, and define events that determine the logic of your gameplay.