Linux

Unix Speech Recognition - Special Synapse TAP Workstation translates speech into mouse events and keystrokes to control all environments - Unix, mainfame, and Mac with speech recognition.
http://www.unixspeech.com/

Open Mind Speech Project - Speech recognition project for Linux. Designed so that it can be easily integrated into any application or window manager as well as the KDE and Ggnome desktop environments.
http://freespeech.sourceforge.net/FreeSpeech/html/

The Festival Speech Synthesis System - 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.
http://www.cstr.ed.ac.uk/projects/festival/

The MBROLA Project - Multi-lingual text to speech synthesis. Free multi platform software download for research purposes.
http://tcts.fpms.ac.be/synthesis/

CVoiceControl - CVoiceControl is a speech recognition system that allows the user to connect spoken commands to Unix commands.
http://www.kiecza.net/daniel/linux/