Herrie is a command line music player. It has a split-screen file manager and playlist interface and supports a number of file formats (MP3, Ogg Vorbis, wave, FLAC, etc). It also has some nice features, including a chroot() function for untrusted setups (remote logins, parties, etc). AudioScrobbler is also implemented using Curl.
Lyra is a front-end to the Music Player Daemon (MPD). Based loosely on the Creative Media Source software, it has the aim of supporting large collections of albums and artists. Other interesting features are the implementation of a local cache of the music library using an SQLite database, increased speed, and flexibility. In addition, Lyra supports integration with the Last.fm service, which includes "Scrobbling" and album cover art.
Apple's QuickTime multimedia architecture has some features that can be exploited through server-side scripting and HTML embedding, but it's something of a black art. There is confusion and inconsistency in how best to embed QuickTime in Web pages, deal with QTVR, let movies talk to each other, pass XML QTLists back and forth between movies and servers, and much more. PEAR::QuickTime hopes to expose this in a clean and elegant way so that QuickTime can reach the audience it deserves. It aims to provide a simple and consistent interface to these features through a set of PEAR-compatible PHP classes and functions.
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.
The PKSampler is a live DJ tool. It is different from other "live DJ tools" in that it focuses on allowing the user to mix many samples at once. The focus is on a simple touchscreen interface that allows quick access to user-supplied loops and samples. The user interface is driven by Python and Qt, and uses 3d POV-ray images for widget animations.