Makes preloading singletons in Unity as easy as marking a class with an attribute
Via Unity Package Manager add from git url
https://github.com/SmallTailTeam/Unity-Preload.git
[Preloaded("Optional name")]
public class ASingletonObject : MonoBehaviour
...And that's it, an empty object with this MonoBehaviour attached to it will be instantiated and DontDestroyOnLoaded as soon as the game starts.
Though be aware that this thing is not well tested yet, and perhaps will be extended in future to support multiple use cases.