I want to develop mobile game using monogame. Is it necessary to use xamarin? Can I create game without xamarin, like in unity3d? Thanks for answers.
Some of the platforms that you can target with MonoGame:
You can use .Net to target Windows and thus no need for Mono or Xamarin
You can use the non-commerical version of Mono to target OS-X using the older (open-source) MonoMac and OpenTK, or if you need access to more of the current OS-X apis, than an Indie (or higher) License of Xamarin.Mac would be needed.
You would need an Indie (or higher) License of Xamarin.iOS and/or Xamarin.Android
Of course, you can get a 30-day trail of Xamarin to play around with.