To create a Xamarin.Mac app that runs without mono installed, check the "Include Xamarin.Mac project" when creating your app using the Eto add-on in VS 2017 or VS for Mac.
Then, compile "YourAptlyNamedApp.XamMac" on a Mac using VS for Mac (yes, you need a Mac). You can distribute the .app and optionally generate a .pkg for users to install the app. Take a look at project options > Mac build for options on what you can do.
As for creating a standalone .app on Windows or Linux, the develop branch of Eto.Forms (2.5) can use mkbundle to embed mono in the generated .app when compiling for Release mode, that is if mono is installed. You can use the pre release nuget packages from the myget feed to try it out.
Hope this helps!