The `GameSystems` MonoBehaviour is the singleton and contains code to access the systems in the game from one location.

GameSystems.cs

public class GameSystems : MonoBehaviour
{
	private static GameSystems _instance;

	public static GameSystems Instance
	{
		get
		{
			if (_instance == null)
			{
				_instance = GameObject.FindObjectOfType<GameSystems>();
				if (_instance == null)
				{
					var go = new GameObject("__GAMESYSTEMS__");
					_instance = go.AddComponent<GameSystems>();
					_instance.Cloud = CloudFactory.Create();
					_instance.FileIO = FileSystemFactory.Create();
				}
			}
		}
	}

	public ICloudService Cloud { get; private set; }

	public IFileSystem FileIO { get; private set; }
}