AppStream is a collaborative effort for making machine-readable
software metadata easily available to programs that need it.  It
is part of the Freedesktop ecosystem and provides a convenient way
to retrieve information about available software, making it one of
the building blocks for modern software centers.

AppStream consists of a specification to describe individual software
component metadata in XML (so-called MetaInfo files), as well as
a derived specification for a metadata-collection format to provide
a list of these metadata entries in XML or YAML for easy consumption
by software centers and other tools which need to know about
available software in a repository.  In addition to the metadata
specification, AppStream specifies a set of related features to
help providing better metadata for software repositories (primarily
in Linux distributions).  This reference implementation of AppStream
provides a shared library to work with these metadata files, features
to index and query their data quickly, as well as other useful
related functionality to make building programs which work with
software metadata very easy.