Sonata is a slick GTK+ GUI controller for the Music Player Daemon audio player which has not been updated since 2009. It is and has been unmaintained for a long time. It is, as such, no longer included in many Linux distributions.
Why you'd want it
Music Player Daemon is a nice daemon which runs in the background locally on a remote server and plays music. Various GUI's (and console apps) for controlling it exist. Sonata was the slickest one available for a long time.
Sonata is based on the now unmaintained Pygmy MPD GUI by Andrew Conkling and Matthew G. Sonata developer Scott Horowitz story is that Sonata was forked from Pygmy "in order to fix bugs, introduce new features, and proceed down a different path".
Someone needs to pick up the torch
The Sonata github page at https://github.com/multani/sonata/ states that
"I (@multani) don't use Sonata much anymore and as a consequence, I've been very slow to answer even to the few bugs reported and pull requests from external contributors.
If you are still interested in Sonata and would like to see it alive again, please contact me by email to see what we can do!"