HASAS (HydroAcoustic Signal Analysis System) is a modular system for passive sonar signal analysis. It can be used for biological research or surveillance, for example. The soundcard is used as input device, and it currently includes all the very basic functionality; beamformed audio, direction finding, level histogram, LOFAR/DEMON (narrowband spectrogram), wideband spectrogram, and raw audio.
MPEG Maaate (MPEG audio analysis toolkit) is a C++ toolkit to parse and analyse audio data in the frequency domain, e.g. analysing MPEG-1/2 Layers 1-3 audio files in the compressed domain. It makes the encoded fields of an MPEG audio stream accessible and provides some content analysis functions like silence detection.
Synaesthesia is an eyecandy program that represents music graphically in real time as coruscating fields of fog and glowing lines. It is intended as a visual accompaniment to music. Its display combines information about the frequency, location and diffuseness of sound. It can take input from CD, line, piped from another program, or from EsounD. It also functions as a CD player.
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.