JSONMessage is a JSON-centric client/server messaging API. It originated from a JavaScript/PHP5-based framework, but has since evolved to include a Java implementation as well. The project is mostly about defining messaging conventions, which can then be implemented using arbitrary technologies.

You can read all about JSONMessage on the HomePage.

Project Stats provided by Ohloh.net:

Note: though the harvested statistics suggest (correctly) that most of the code is Java, the project is actually JavaScript-centric. The fact that most of the lines of code are Java is an accident of evolution, and has little to do with Java's role in this project.