I love developing small but nice mobile games. Predominantly for iOS, but since SpriteKit and SceneKit show borders, I have opted for an engine. Godot Engine is open source, that makes that engine so valuable to me.
Anyone looking for an alternative to Unity can recommend the Godot Engine. Even though the Godot engine is not so well known, there are already some games that were developed with Godot.
I am still at the beginning of learning the Godot Engine, but I am happy to develop beautiful games. The wonderful thing is that you can write a code and compile the game, for example for iOS and Android.
Godot Engine is open source, without restrictions and without fees. So I think that Godot has a better stand over Unity.