Beets is a media library management system designed for obsessive-compulsive music geeks. It catalogs your collection, automatically improving its metadata as it goes using the MusicBrainz database. It also downloads cover art for albums it imports. Then it provides a bouquet of tools for manipulating and accessing your music. Beets also includes a music player that speaks the MPD protocol, so you can play music in your beets library using any MPD client.
Potamus is a lightweight GTK+-based audio player with a simple interface and an emphasis on high audio quality. It tries to make it as easy as possible to use your file manager to locate and play music. Potamus can play a wide range of audio formats, works with ALSA, JACK,and other audio systems, and supports 24-bit audio and gapless playback.
Jaksta Music Miner for Mac automatically captures and tags MP3s from popular audio and video Web sites. Just open Jaksta Music Miner, play a song or video, and the MP3 is created, usually up to 10x faster than real time. The MP3 can be added to iTunes with the click of one button. It supports Grooveshark, Last.FM, YouTube, Jango, and more and is great for discovering new music or enjoying your music offline.
Khövsgöl is a minimal, highly configurable music player and browser. It can easily handle very large collections of music. It's designed for the GNOME desktop, but can run well in other environments. It works fine as a standalone player, but can also be used to remotely control music daemons such as MPD.