SpeakingX

Sphinx 4 is a Java speech recognition system in CMU's sphinx ASR family.
To try out the system, download the binary
for sphinx 4, the setup your environment to support the Java Speech API (JSAPI).
Then run the demo:
java -mx312m -jar bin/HelloWorld.jar
java -jar bin/HelloDigits.jar
java -mx312m -jar bin/HelloNGram.jar
java -jar bin/ZipCity.jar [-continuous]

HTK
license: prohibits redistribution and commercial use, but using HTK to train models in commercial R&D is allowed (http://htk.eng.cam.ac.uk/docs/faq.shtml)
Development Language: C
Latest release: 3.4 (13 December 2006) http://htk.eng.cam.ac.uk/download.shtml, registration (free) required.
Platform: cross-platform, can be built on linux/unix, Mac OS X, and Windows
Support: well known HTKbook, active mailing list

Sphinx

license: BSD