GNUdap is a project to build a userspace driver to interface Linux with proprietary-protocol USB MP3 players and mass storage devices. Currently, GNUdap supports only the "Perstel,Inc. CHIC MP10". GNUdap is also an experiment to test the advantages of a strongly-typed programming language and of the functional programming paradigm in hardware development. GNUdap currently supports all features supported by the official program provided with the Chic, and has some additional features, like being able to transfer MP3s directly to the PC.
Liquidsoap is a powerful tool for building complex audio streaming systems, typically targetting Internet radio stations. It consists of a simple script language, which has a first-class notion of source (basically a stream) and provides elementary source constructors and source compositions from which you can build the streamer you want. There is no constraint on the streams, in contrast to many other tools which can only stream one file after another. Moreover, it is not restricted to a single stream. Finally, it interfaces well with external tools.
Mp3tag is an Objective-Caml library for reading and writing ID3v1 and v2 tags in MP3 files. It includes mp3tag tools, which can be used to modify tags in MP3 files or rename files according to their tags, and a cddbtag tool that modifies tags by using a CDDB server to retrieve information about the track.