wxMusik is a fast and lean music library player for Windows and Linux. It supports MP3, MP2 , Ogg, APE, MPC, and FLAC, WAV, and AIFF formats on all platforms and WMA on Windows. It features powerful dynamic playlists that use SQLite, supports listening to Icecast and Shoutcast streams in a reliable manner, and has a nice cross-fading feature and a really cool autodj feature.
iTunes Export provides the ability to export iTunes Playlists to the standard .m3u file format. Unfortunately, this feature is not included in the iTunes application and is extremely useful for users who wish to use iTunes with other applications or devices. iTunes Export is written in C# (.Net). iTunes Export provides a Command Line version (tested on Mono) and a GUI version, as well as a library that developers can use in their own applications.
Thump (The Unix MP3 Player) is a flexible and modular set of MP3 playing daemons written in Python. The daemons communicate with each other and the rest of the world via XML, and playlist management is handled by a combination of standard file manipulation utilities (such as find) and regular expressions.
Webplayer is a Borges-based, Web browser-controlled MP3 player. Webplayer features a file browser that can load or recursively load from a directory of MP3 files. It also provides simple playlist control and volume control (tested on FreeBSD). Components of Webplayer can be launched into separate windows or used in one big main window. Webplayer incorporates portions of Yoshinori Toki's rmp3.
musutil includes several utilities for working with a music collection. The principle one is musview, which generates a number of "Views". Each View, analogous to a database view, is an alternative presenation of the original files. The View can selectively include only some files (based on their properties) or have files processed into into a different format, with audio filters applied, adjusted tag data, or a different filename.
Podtool is a Python-based utility for managing tracks between a local music repository and an iPod. In particular, it implements correct playcount and ratings synchronisation, which is important when using smart playlists. If you've used iTunes and selective smart playlist synchronisation, then you know what this does.