protobuf (Google's data interchange format)

Protocol buffers are a flexible, efficient, automated mechanism for
serializing structured data, think XML, but smaller, faster, and
simpler. You define how you want your data to be structured once,
then you can use special generated source code to easily write and
read your structured data to and from a variety of data streams
and using a variety of languages. You can even update your data
structure without breaking deployed programs that are compiled
against the "old" format.
