====== Concepts and Relationship ======

  * For C#, there are 2 main popular free IDE softwares
    - **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)
    - **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