GData

GData (Google Data Protocol) provides a simple protocol for reading and writing data on the Internet, designed by Google. GData combines common XML-based syndication formats (Atom and RSS) with a feed-publishing system based on the Atom Publishing Protocol, plus some extensions for handling queries. It relies on XML or JSON as a data format.

Google provides GData client libraries for Java, JavaScript, .NET, PHP, Python, and Objective-C.

Implementations
An implementation called libgdata written in C is available under the LGPL license. * https://git.gnome.org/browse/libgdata/tree/