Emacspeak is the first full-fledged speech output system that will allow someone who cannot see to work directly on a UNIX system. Emacspeak is built on top of Emacs. Once you start emacs with emacspeak loaded, you get spoken feedback for everything you do. Your mileage will vary depending on how well you can use Emacs.
empegify is a networkable system for creating MP3s. It is designed so that you can perform the ripping on one set of machines, the encoding on another, storing the data to a final machine. It features CDDB support and maintainable code. It also includes a simple Web interface for easy monitoring.
eXtace is a visual sound display/analysis program. It requires Esound (esd) for its audio source. It includes various fast fourier transforms of the audio data in realtime. Its displays include a 3D wireframe flying landscape, a 3D textured flying landscape, a 16-256 channel graphic EQ, three types of scopes, a 3D "spike" flying landscape, and two forms of spectragrams. The 3D traces can be picked up, manipulated, and displayed at nearly any angle. eXtace also features a 3D direction control widget for controlling the angle and speed at which the trace runs away and a gradient/colormap editor for changing the colormap to suit your needs. No OpenGL is required.
mp3riot (formerly known as f2html.pl) is a command line utility that searches recursively through directories, builds a file list (with additional file information), and generates HTML files, playlists, etc. The output can be controlled, links can be corrected, and more. The script is mainly desigend to create Web pages, playlists, and databases for MP3 and Ogg files, but can also used for other purposes.
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.
The festvox project, based at Carnegie Mellon University, distributes documentation, scripts, and examples that should be sufficient for an interested person to build her own synthetic voices in currently supported languages or new languages in the University of Edinburgh's Festival Speech Synthesis System. The quality of the result depends much on the time and skill of the builder. For English, it may be possible to build a new voice in a couple of days' work; a new language may take months or years to build.