Godot (C#, GDScript, visual). By far the most-mentioned alternative to Unity, Godot seems in many ways to be an open-source response to Unity: less focused on high-end engine features than something like Unreal, and more focused on being quick and easy to spin up for beginners. Common complaints seem to be that it is \u201Cnot quite there yet\u201D \u2014 perhaps because of bugs and missing features compared to Unity \u2014 and that it lacks first-class support for consoles, a feature most professional game developers now need. But it has been used in some recent notable games (Brotato and Dome Keeper), and it seems to have decent momentum behind it.