Todos Free for linux.

gnome (& ubuntu): http://live.gnome.org/GnomeVoiceControl
ubuntu: https://wiki.ubuntu.com/SpeechRecognition
gnome demo in br: http://raphaelnunes.wordpress.com/2007/06/16/gnome-voice-control-demonstration/

open mind: http://freespeech.sourceforge.net/
sphinx: http://cmusphinx.sourceforge.net/html/cmusphinx.php
voxforge: http://www.voxforge.org/
julius (japonês): http://julius.sourceforge.jp/en_index.php
spx download: http://linux.softpedia.com/get/Programming/Libraries/Speech-Recognizer-SPX-Server-13710.shtml

fontes de vários:
http://tldp.org/HOWTO/Speech-Recognition-HOWTO/index.html
http://en.wikipedia.org/wiki/Linux_speech_recognition_software
http://volker.dnsalias.net/linux/speechrec.html (viavoice)