MPD or Music Player daemon is one of the oldest open source music player servers. It can be installed on Windows, OSX or Linux. Once installed, it can be controlled by a client to play music on the server using a client that interfaces with the server.
Numerous clients are available for MPD ranging from phone or comptuer apps on a variety of platforms. A few years ago, I transformed an old router into an internet radio that used mpd to play music from internet radio stations.
Today, there are many music player distros that one may install on the raspberry pi or an old PC such as Volumio and Runeplayer. These run an MPD server under the covers and present very user friendly screens for music playing on the front end or when accessed by their web interface.
Today, I have an MPD daemon that runs on the same computer that runs my home automation system in my study. It is connected to Audioengine A2+ White (Pr.) 2-way Powered Speaker System. The same computer also runs an Apache server with Rompr, my favorite MPD client.
I also have a Rune player on my Raspberry Pi 3 Model B in my garage that also doubles as my home gym.