GNUMP3d is a streaming server for MP3s, OGG vorbis files, movies and other media formats.
It is designed to be:
* Small, stable, portable, self-contained, and secure.
* Simple to install, configure, and use.
* Portable across different varieties of Unix, the GNU Operating System, and Microsoft Windows platforms.

Mp3 Tag Tools v1.2(C) 2003 John George K. is GNU GPL free software, intutive ID3v1.1 and ID3v2.x mp3 tag editing utility, with several features such as Mass ID3 tagging, Write ID3 tags from Filenames and Rename Files from ID3 tags using Custom Formats, Copy/Synchronize ID3 tags, Cleaning Filenames and Correcting their case, Create ID3 tags using Directory Formats, Create Directories and organize mp3s from ID3 tag info, Export ID3 tag data, Lyrics and Picture tagging, accurately read all MPEG info and append bitrate and mode to filenames. All these tag operations can be carried out  with or without directory recursion.

MusicBrainz is a community music metadatabase that attempts to create a comprehensive music information site. You can use the MusicBrainz data either by browsing this web site, or you can access the data from a client program — for example, a CD player program can use MusicBrainz to identify CDs and provide information about the CD, about the artist or about related information. You can also use the MusicBrainz Tagger to automatically identify and clean up the metadata tags in your digital music collections. 

GramoFile is a computer program, running under the Linux operating system (and some other UNIX-like OSses -- and even DOS/Windows now!), with the main goal of putting the sound of for example gramophone records on CDs. It is able to record hours of CD quality music, split long sound files in separate tracks, and remove ticks and pops from recordings.
This program was originally written by Anne Bezemer and Ton Le as a study project at the department of Information Technology and Systems (sub-department Electrical Engineering) of the Delft University of Technology, The Netherlands. However, development has continued after the end of the project, resulting in the program as it is now.

FFmpeg is a collection of software libraries that can record, convert and stream digital audio and video in numerous formats. It includes libavcodec, an audio/video codec library used by several other projects, and libavformat, an audio/video container mux and demux library. The name of the project comes from the MPEG video standards group, together with "FF" for "fast forward".

JAZZ++ is a full featured, audio capable midi sequencer for Linux and Windows. JAZZ++ offers a lot of functions normally only found in expensive sequencer software, and is used by professionals and hobby musicians all over the world.

Mixere is a free, open-source application for mixing audio files. It runs on Windows NT/2000/XP, and supports WAV, AIFF, MP3, Ogg Vorbis, Flac, and Mod audio files.

Mixere is optimized for live performance, and especially for creating live sound collage. Conceptually, it’s like a rack full of CD players connected to an automated mixer. Mixere's features include dynamic looping of audio, auto-triggering of audio, fully automated sliders, "soft" (gradual) mute/solo operations, crossfading between documents, and unlimited undo.

Open Sound World, or OSW, is a scalable, extensible programming environment that allows musicians, sound designers and researchers to process sound in response to expressive real-time control. OSW combines a familiar visual patching paradigm with solid programming-language features such as a strong type system and hierarchical name spaces. OSW also includes an intuitive model for specifying new components using a graphical interface and high-level C++ expressions, making it easy to develop and share new music and signal-processing algorithms.

split3pm is a tool to extract music segments from a larger MP3 file. For example, you might have a long radio capture in MP3 format and you want to cut out a piece of music from it. Before split3pm you would have had to convert the file to Wave and edit it there; now, you can just tell split3pm the time and duration of one or more audio segments and it will extract the files for you.

split3pm has been tested with very large MP3 files (up to 8 hours long), and is much faster for its purpose than any Waveeditor out there. split3pm is Open Source freeware and is available for both Win32 and Linux.

BonkEnc is a CD ripper, audio encoder and converter for various formats. It can produce MP3, MP4/M4A, Ogg Vorbis, AAC, Bonk and FLAC files and features full Unicode support, including support for UTF-8 freedb entries.