Microsoft Visual Studio is a fully-featured, extensible, free integrated development environment (IDE) from Microsoft. It is used to develop computer programs for Microsoft Windows, as well as web sites, web apps, web services and mobile apps. C# gets really fun due to the simplicity and robust graphical features that Visual Studio offers, all for free in the community edition.
MonoDevelop enables developers to quickly write desktop and web applications on Linux, Windows and macOS. It also makes it easy for developers to port .NET applications created with Visual Studio to Linux and macOS maintaining a single code base for all platforms.
All that is done by the 
Mono project which is "an open-source port of the .NET framework, It is most commonly used to run .NET under Linux", that was developed by the software company named Xamarin.
Xamarin Studio is an open source app platform from Microsoft for building modern & performant iOS and Android apps with C# and .NET.
(Xamarin was bought by Microsoft and its products "Xamarin Tools" a now part of 
Microsoft Visual Studio)
.NET IDE based on the IntelliJ platform and 
ReSharper, Supports C#, ASP.NET, ASP.NET MVC, .NET Core, Unity and Xamarin.
Small Basic is the only programming language created specially to help students transition from block-based coding to text-based coding. By teaching the fundamental elements of syntax-based languages in an approachable manner, Small Basic gives students the skills and confidence to tackle more complex programming languages such as Java and C#. You can also build applications for Kinect, Lego Mindstorm, Raspberry Pi, Arduino, Oculus Rift, and more using Small Basic.
While Visual Studio, and other IDEs, are powerful tools, they can sometimes hinder productivity more than they promote it. You don’t always need, or want, the overhead of a creating a new solution or project. Sometimes you want to just type away in your favorite text editor. "scriptcs" frees you from Visual Studio, without sacrificing the advantages of a strongly-typed language.
Stadium is a web application builder which generates a fully portable and customisable ASP.net, MVC application. Use the drag-n-drop designer to build your application and host it on any server (IIS required). The power of Stadium lies in the fact you can connect to your database and provide a UI for people to view and manage your data directly and securely.
