My understanding is that Mono is being billed as a client framework (Monogame, Xamarin, Unity, Blazor) while Core is more for the server/systems target. To add to the confusion, ".Net Standard" is a library compilation target that should work everywhere (even the legacy Windows-only .Net Framework). Interestingly, the newly MIT-licensed Xenko game engine compiles to .Net Standard libraries which is how it supports so many platforms (via barebones launcher/shim projects for whichever framework implementation is desired). Edited for clarity, thx.