AppStream is a cross-distribution effort for enhancing the way we
interact with the software repositories provided by Linux distributions
by standardizing software component metadata.
It provides the foundation to build software-center applications,
by providing metadata necessary for an application-centric view on
package repositories. AppStream additionally provides specifications for
things like an unified software metadata database, screenshot services
and various other things needed to create user-friendly
application-centers for (Linux) distributions.