This library is basically "stolen code" from MvvmCross Messenger Plugin removing any dependency on MvvmCross so it can be used in any kind of project.
Check out their docs here: https://github.com/MvvmCross/MvvmCross/wiki/MvvmCross-plugins#messenger
All credits to the great MvvmCross team and my coworker rfrailemartinez who gave me this code base