That's all I know that Xamarin makes, so I think this article is going a bit over my head, but it'll be a shame if I suddenly need a Microsoft account to use it. I do like diversity in my language tooling.
Last I checked, that was just a forked and rebranded Mono Develop with Xamarin's main product line (iOS and Android support for .NET) bundled in.
Xamarin Studio is a swiss army knife. I don't know about your use case, but I use it under the name Monodevelop on linux (not really sure what that association is) and as Xamarin studio on windows. For my use case, it's a C# and C++ IDE for desktop development, same as visual studio.
It's certainly not a MacOS only product, it supports all three platforms including windows.
Mono only supports a subset of the whole stack.
No sane .NET developer would use Mono on Windows, its purpose is .NET portability to other OSes.
WHY ARE WE ARGUING?
explodes