Festival is a general multi-lingual speech synthesis system developed at CSTR. It offers a full text to speech system with various APIs, as well an environment for development and research of speech synthesis techniques. It is written in C++ with a Scheme-based command interpreter for general control.
KegTracker is a GTK+-based MOD editor for Linux distributed under the terms of the GPL. It uses a modified version of the xmp library by Claudio Matsuoka and Hipolito Carraro Jr. KegTracker and can play all music modules supported by xmp, which is just about everything except Impulse Tracker modules. Its graphical interface includes Track Display, Order Display, Instrument and Sample Display, as well as basic controls you'd expect in a tracker. It also features a cool starfield about box by Rasterman.
Libmmoss enables the Linux version of Netscape Navigator/Communicator to play sounds from Java applets. It is a replacement for Netscape's implementation of (the Java class) sun.audio.AudioDevice (including some JRI native C code). It should work with either the OSS or ALSA sound drivers. The latest version will also work with EsounD.
SoundTracker is a pattern-oriented music editor (similar to the DOS program 'FastTracker'). Samples are lined up on tracks and patterns which are then arranged to a song. Supported module formats are XM and MOD; the player code is the one from OpenCP. A basic sample recorder and editor is also included.
STK is a set of audio signal processing C++ classes and instruments for music synthesis. You can use these classes to create programs which make cool sounds using a variety of synthesis techniques. This is not a terribly novel concept, except that STK is very portable and completely user-extensible.
Xoscope (or oscope) is a digital oscilloscope using input from a sound card or EsounD and/or a ProbeScope/osziFOX. Its features include 8 simultaneous signal displays, 1 us/div to 2 s/div time scale, built-in and external math functions including inverse, sum, diff, avg, xy, and FFT, 23 memory buffers, 5 automatic measurements, and file save/load.
Cdrdao records audio/data CD-Rs in disk-at-once (DAO) mode based on a textual description of the CD contents (toc-file). Features include full control over length and contents of pre-gaps (pause areas between tracks). Pre-gaps may be completely omitted, e.g. for dividing live recordings into tracks. Control over sub-channel data like catalog numbers, copy, pre-emphasis, 2-/4-channel flags, ISRC code, and index marks are provided as well. GCDMaster is a Gnome GUI front-end that lets you import MP3 and WAV files, select track markers and cut/copy/paste audio snippets before burning.