Starling is the "Cross-Platform Game Engine", a popular Stage3D framework.
You can easily install Starling using haxelib:
haxelib install starling
To add it to an OpenFL project, add this to your project file:
<haxelib name="starling" />Clone the Starling repository:
git clone https://github.com/openfl/starling
Tell haxelib where your development copy of Starling is installed:
haxelib dev starling starling
To return to release builds:
haxelib dev starling