Nifty GUI is a Java Library that supports the building of interactive user interfaces for games or similar applications. It utilizes OpenGL for rendering and it can be easily integrated into many rendering systems. The configuration of the GUI is stored in xml files with little supporting Java code. In short Nifty helps you to layout stuff, display it in a cool way and interact with it :)

Lots of Nifty example code! You can find the source for nearly all demos/tutorials in here.

Nifty Controls

jMonkeyEngine is a 3-D game engine for adventurous Java developers

Nifty Renderer for LWJGL

This is an OpenAL/lwjgl based SoundDevice for Nifty GUI. It was extracted out of Slick2D to be independent of the whole Slick2D library and to be used with none Slick2D based renderes.

Nifty Examples For LibGDX Main Core

Nifty Renderer for Slick2D

Nifty Sound Device for Pauls-Soundsystem

Nifty Renderer for JOGL

JME3 NiftyGUI