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.
Baudline is a time-frequency browser designed for scientific visualization of the spectral domain. Signal analysis is performed by Fourier, correlation, and raster transforms that create colorful spectrograms with vibrant detail. Conduct test and measurement experiments with the built in function generator, or play back audio files with a multitude of effects and filters. The baudline signal analyzer combines fast digital signal processing, versatile high speed displays, and continuous capture tools for hunting down and studying elusive signal characteristics.
BpmDj is a program that can be used by a DJ. It plays MP3 and Ogg files. It has a fully automatic BPM counter. It can determine the sound color. It has a full fledged Qt based interface. It will help you manage a large amount of songs. It can help in creating playlists and has proven to be very robust. The program also allows offline automatic mixing and contains a wavelet based beat graph analyzer to visualize audio tracks.
FMS is a tool to create all kinds of sounds from scratch. You can play any sound (sine, triangular, vowels, etc.) with any property settings (frequency, volume, balance, sweep, etc.) and modulations thereof. It also features tools to save sounds, play .MUS music, graphically display sounds, and make real noise.
IMMS (Intelligent Multimedia Management System) is an intelligent playlist framework that tracks your listening patterns and dynamically adapts to your taste. It is incredibly unobtrusive and easy to use as it requires no direct user interaction. Plugins are currently available for XMMS and BMP.
KPlaylistCreator is a jukebox for KDE. It scans for MP3 and Ogg Vorbis files, located in various directories, creates a unique tree view with genre, artist, album, and song title information, features a user rates mechanism, a user playlist manager, and a wizard playlist creator, edits tags for both MP3 (ID3 v2) and Ogg Vorbis files, checks directories for new and missing files automatically, sends playlists to a directory, XMMS, or to K3B, displays and sets the album art of MP3 files, creates playlists from a virtual library, and includes popup windows to indicate change of song.