Napster!

Clementine is a cross-platform free and open source music player and library organizer. It is a port of Amarok 1.4 to the Qt 4 framework and the GStreamer multimedia framework, focusing on a fast and easy-to-use interface for searching and playing your music. It is available for Unix-like, Windows and Mac OS X.

Google Play Music, a service available for people who have a Google account, lets people upload their personal music collection and access it instantly on the web or any compatible device.

Manage your music as a library, as playlists or as folders on the file-system. Organize, browse and find music on your computer, on portable devices and on the web. Small or large collections are handled with ease.

Rhythmbox is an audio player for Linux that plays and organizes digital music. Inspired by Apple's iTunes, it is free software that is designed to work well under the GNOME Desktop using the GStreamer media framework.

Amarok is a powerful music player for Linux, Unix and Windows with an intuitive interface. It makes playing the music you love and discovering new music easier than ever before - and it looks good doing it!

Play your music and videos. Stay entertained and up to date with podcasts and video podcasts. Discover new music with Last.fm radio. Sync your G1 phone, iPod, and other devices.

Quod Libet is a Gapless GTK+-based audio player written in Python. Its designed around the idea that you know how to organize your music better than we do. It lets you make playlists based on regular expressions (dont worry, regular searches work too). It lets you display and edit any tags you want in the file. And it lets you do this for all the file formats it supports - Ogg Vorbis, FLAC, MP3, Musepack, and MOD.

It just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features & support for all audio formats you should ever need.

gPodder downloads and manages free audio and video content ("podcasts") for you. Listen directly on your computer or on your mobile devices.

JetAudio is integrated, multimedia software made of a single compact rack. Not only does it play various music and video files, it also has features such as CD burning, recording, and conversion to other file formats. You can create your own Internet broadcast by using JetCast, provided with JetAudio, and you can play all major file formats, including WAV, MP3, MP3Pro, OGG, WMA, MPEG, AVI, WMV, MIDI, RM, and video and audio CD tracks.