We just migrated our Wiki to Github, so it's a little bit rough, we'll fix things up in the next days
Libgdx is a cross-platform Java game development framework based on OpenGL (ES) that works on Windows, Linux, Mac OS X, Android, your WebGL enabled browser and iOS.
Head over to http://libgdx.badlogicgames.com/documentation.html to find the latest getting started guide, download links and so on. You can find more information on libgdx on our official site at http://libgdx.badlogicgames.com/
You can get the latest release or nightly version of libgdx from the offical download site. We actually recommend using the nightlies to be up to date with latest bug fixes and feature additions.
The Wiki contains all the information you'll need to write a libgdx game. You can contribute to the Wiki directly here on Github!
We also provide Javadocs online. The Javadocs are also bundled as source Jars with every libgdx distribution for consumption in your favorite IDE.
You can get help on our forum and talk to other libgdx users on our IRC channel #libgdx at irc.freenode.net.
Libgdx has a strong developer community constantly improving the code base. We love to get any and all help we can. The Contributing article describes the process of helping libgdx to become even better.
To contribute, you need to work with libgdx' sources directly, something normal users do not have to go through. The Working with the Source article will give you directions.
Libgdx is licensed under the Apache 2 License, meaning you can use it free of charge, without strings attached in commercial and non-commercial projects. We love to get (non-mandatory) credit in case you release a game or app using libgdx!