Concepts and Relationship

For C#, there are 2 main popular free IDE softwares
1. Microsoft Visual Studio community edition
  - https://www.visualstudio.com/products/free-developer-offers-vs
  - features:
    - license: free for small team or individual
    - available only on windows system
    - use .NET framework (only works on windows system)
    - use Xamarin framework (free for small team or individual)
    - support other language dev like python, javascript, c++ …
    - support extended development in other software like game engines (Unity, Epic)
2. MonoDevelop (aka Xamarin Studio in win, mac)
  - http://www.monodevelop.com/download/
  - features:
    - license: open source and free for all
    - available on Windows, Mac OS X, Linux
    - use .NET framework or Mono framework (opensource port of .NET) on windows, and Mono framework on Mac OS X and Linux
    - use Xamarin framework (free for small team or individual on Windows and Mac only)
    - c# and .NET related language only
    - use GTK# as GUI library

Xamarin Framework / Xamarin platform
- license: free for small team and individual
- https://www.xamarin.com/platform
- enable you to write application using C#, and transcode it to native code and native GUI and run on many operation system
  - including mobile: iOS system, Android system, Windows phone system
  - including desktop: windows, mac os x
  - no linux support because too many variation Linux system

Mono Framework and GTK# GUI library
- license: open source and free for all
- http://www.mono-project.com/download/
- http://www.monodevelop.com/
- enable you write .NET compatible C# code and run application in all desktop system like Windows, Mac OS X, Linux