Mapsui.Forms
Mapsui can be used on Xamarin.Forms with the Mapsui.Forms nuget package.
Mapsui.Forms is a 'native' Xamarin.Forms implementation, meaning it does not use Xamarin.Forms Renderers around platform specific components but implements a Xamarin.Forms implementation instead.
Mapsui.Forms uses SkiaSharp.Views.Forms to display the map on the device. This works for iOS, Android, UWP and Mac OS. On WPF there still is an issue with placing controls over the Map.
To get started see getting started with Xamarin.Forms.