OwnTone is an open source (audio) media server for GNU/Linux, FreeBSD and macOS.

It allows sharing and streaming your media library to iTunes (DAAP1), Roku (RSP), AirPlay devices (multi-room), Chromecast and also supports local playback.
You can control OwnTone via its web interface, Apple Remote (and compatible DAAP/DACP clients), MPD clients or via its JSON API.
Besides serving your local music, podcast and audiobook media files, OwnTone supports internet radios and Spotify (requires Spotify premium account).

• OwnTone @ GitHub.

mpris media player command-line controller for vlc, mpv, RhythmBox, web browsers, cmus, mpd, spotify and others.

Playerctl is a command-line utility and library for controlling media players
that implement the MPRIS D-Bus Interface Specification.
Playerctl makes it easy to bind player actions, such as play and pause,
to media keys.
You can also get metadata about the playing track such as the artist and title
for integration into statusline generators or other command-line tools.

Mopidy is an extensible music server written in Python.
It plays music from local disk, Spotify, SoundCloud, TuneIn, …
Users can edit the playlist from any phone, tablet, or computer
using a variety of MPD and web clients.

• Mopidy @ GitHub.
• Mopidy-MPD
  (Mopidy-MPD @ GitHub)
  is a Mopidy extension for controlling playback from MPD clients
  It's a frontend that provides a full MPD server implementation to make Mopidy
  available from MPD clients.

Festival, a music player.

Festival is a music player for local album collections.

Festival @ GitHub.