Libgdx is a Java game development framework that provides a unified API that works across all supported platforms.
The framework provides an environment for rapid prototyping and fast iterations. Instead of deploying to Android/iOS/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.
That is most useful java game framework. Pure Java and bit of C meets perfection.