Audacity is a cross-platform multitrack audio editor. It allows you to record sounds directly or to import Ogg, WAV, AIFF, AU, IRCAM, or MP3 files. It features a few simple effects, all of the editing features you should need, and unlimited undo. The audio I/O uses PortAudio, which fully supports OSS, Mac OS X CoreAudio, and Windows WMME, and can be compiled with support for ALSA and Jack.
MP3 Diags finds problems in MP3 files and helps the user fix many of them. It looks at both the audio part (VBR info, quality, normalization) and the tags containing track information (ID3). It has a tag editor, which can download album information (including cover art) from MusicBrainz and Discogs, as well as paste data from the clipboard. Track information can also be extracted from a file's name. Another component is the file renamer, which can rename files based on the fields in their ID3V2 tag (artist, track number, album, genre, etc.).
The FAAC project includes the AAC encoder FAAC and decoder FAAD2. It supports several MPEG-4 object types (LC, Main, LTP, HE AAC, PS) and file formats (ADTS AAC, raw AAC, MP4), multichannel and gapless en/decoding as well as MP4 metadata tags. The codecs are compatible with standard-compliant audio applications using one or more of these profiles.
Streamripper records MP3, Ogg, AAC, and NSV audio and video files from Shoutcast and Icecast compatible streams. The streams can be recorded as a whole or in individual tracks. Streamripper also features a relay stream, which lets you listen or watch live from multiple clients while recording.
Mixxx is software for DJs that provides everything needed to create live mixes. It allows you to beatmatch songs and crossfade them together, like you would with turntables and a mixer. It runs without any extra hardware, and offers a wide range of advanced features including comprehensive MIDI controller and vinyl control support. To obtain the lowest latency and highest responsiveness, it uses hardware video acceleration and takes advantage of multi-core CPUs.
cmus is a small, fast, and powerful console music player for Linux and *BSD. It supports almost all common file formats, SHOUTcast/Icecast streaming, and multiple output plugins. cmus features multiple media library views, a playqueue, a directory browser, powerful filters, and vi-style search and keybindings. It also features gapless playback, ReplayGain, Unicode support, and customizable color schemes.
Andromeda turns collections of MP3s into fully-featured streaming Web sites. Many other file formats are supported, including: WMA, OGG, MPG, AVI, and WMV. It can be used as a personal jukebox on a local network or over the Internet (bandwidth permitting). It works well with PHP-Nuke, PostNuke, and phpWebSite. Additional features include skins, custom playlists, logons/accounts, and a search tool. Andromeda is also multilingual, speaking English, German, Russian, Dutch, Spanish, and many other languages. No database is required. ASP and PHP versions are available.