Ares (Aural RPG Experience System) is a software to play music and sounds during (pen & paper) role-playing games. You define which music and / or sounds to play when a certain situation occurs in an Editor program. Then, during the game, they are played by a Player program or app and you control which ones to play with a Controller program or app.
You can find out more about Ares on its homepage at http://aresrpg.sourceforge.net/. There you can also download pre-built executables. This site on GitHub is mainly for developers which are interested in the source code and may even wish to contribute to the development of Ares.
The file HowToBuild contains information on how to build the various programs and plugins of Ares. There's also an overview of the various modules in the file Modules.