Libgdx is a Java game development framework that provides a unified API that works across all supported platforms (Windows, Linux, Mac OS X, Android, iOS, HTML5/WebGL).
The framework provides an environment for rapid prototyping and fast iterations. Instead of deploying to iOS/Android/Javascript after each code change, you can run and debug your game on the desktop, natively. Desktop JVM features like code hotswapping reduce your iteration times considerably.
Libgdx tries not be the "end all, be all" solution. It does not force a specific design on you. Pick and choose from the features it provides.
