Cross Platform Free Extensible
You need development toolkit to easily develop game.
Currently, it's contains project and content builder. See more prerequisite installation.
Open terminal or command prompt
run {path-to}\ProjectBuilder.exe new YourProjectName
If you on Mac or Linux environment
run mono {path-to}\ProjectBuilder.exe new YourProjectName
Open YourProjectName.sln
on YourProjectName
directory.
A C# IDE should be open.
On C# IDE, build and run like other C# projects.
These action will download some dependencies, just first time.
If successfully, an empty burlywood color game window will appear.
Read the docs, explore the examples, and create your game.