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Godot Engine
Free and open-source game engine. 2D and 3D, lightweight, no royalties, no strings attached.
Godot is a completely free game engine under the MIT license. Build 2D and 3D games with a dedicated scripting language (GDScript), C#, or C++. The editor is under 50MB, starts instantly, and runs on modest hardware. Export to Windows, Mac, Linux, iOS, Android, Web, and consoles. Unlike Unity and Unreal, Godot has zero fees, zero royalties, and zero tracking. You own everything you make. The community is growing fast and the 4.x release brought major 3D improvements.