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.
A Free and Open Source community driven media server, providing ubiquitous access to your music.
NINJAM is open source (GPL) software to allow people to make real music together via the Internet. Every participant can hear every other participant. Each user can also tweak their personal mix to their liking. NINJAM is cross-platform, with clients available for Mac OS X, Linux and Windows. REAPER (our digital audio workstation software for Windows and OS X) also includes NINJAM support (ReaNINJAM plug-in).
Icecast is a streaming media (audio/video) server which currently supports Ogg (Vorbis and Theora), Opus, WebM and MP3 streams. It can be used to create an Internet radio station or a privately running jukebox and many things in between. It is very versatile in that new formats can be added relatively easily and supports open standards for communication and interaction.