Standards is the new (and revived) version of the former Standards 1.0/2.0 library. It is based in Java, and includes all the basic materials and code necessary to create a basic game.
The version of Standards under the master branch is the public release version. Additionally, the development branch contains test and in-progress code. There may be game-breaking features in these versions, so use them at your own risk.
The API is linked here.
The releases come in the form of .JAR files. Download the .JAR file here, and include it in your project's libraries.