Vexi is a rich GUI platform for creating desktop-like Internet or intranet applications using an intuitive XML/JavaScript API and an extensible widget set with themes, JSON support. Communicate with servers using XMLRPC/SOAP/REST and runs on Java.
...The Efficient XML Interchange (EXI) format is a very compact representation for the Extensible Markup Language (XML) Information Set that is intended to simultaneously optimize performance and the utilization of computational resources.
Besides the EXI library EXIficient provides a command-line interface (CLI, see com.siemens.ct.exi.cmd.EXIficientCMD) and a graphical userinterface (GUI, see http://exificient.sourceforge.net/exificient.jnlp)