Funkwhale is a community-driven project that lets you listen and share music and audio within a decentralized, open network. It can be self-hosted and is libre, open source software.
Ampache is a web based audio streaming application and file manager allowing you to access your music from anywhere, using almost any internet enabled device.
Exaile is a cross-platform music manager and player for GTK+ written in Python and is easily extensible via plugins. It incorporates automatic fetching of album art, handling of large libraries, lyrics fetching, artist/album information via Wikipedia, streaming Internet radio...
A personal music streaming server that works.
If you want to use the mobile apps, you have to pay for it.
Subsonic is a free, web-based media streamer, providing ubiquitous access to your music and video. Use it to share your music with friends, or to listen to your own music while at work. You can stream to multiple players simultaneously, for instance to one player in your kitchen...
Music Player Daemon (MPD) is a flexible, powerful, server-side application for playing music. Through plugins and libraries it can play a variety of sound files while being controlled by its network protocol.
Airsonic is a Free and Open Source community driven media server which allows you to stream, transcode, manage, and share your personal audio from anywhere via an HTML web browser or any number of apps (available for both iOS & Android).
netjukebox is a web-based media jukebox for MPD, VideoLAN and Winamp/httpQ. It features real-time MP3 streaming from different audio formats. Download single tracks or a whole album in one zip file. It is also possible to batch transcode the whole music collection to another...