The following information was written by me one year ago on the Intelligent Multimodal Interfaces course internal forum. Since there are new students in need of fresh info, I reposted it here, make the best of it:
Sphinx Speech Recognition (open source), a cool demo can be seen here (controlling PureData with speech) – also I’ve found this how-to interesting (using python+sphynx, from the same author)
Sphinx4 (rewrite of Sphinx into java – more cross platform), there’s also a pocket version for mobile systems (iphone and so on) – it’s all part of this project from Carnegie Mellon.
eSpeak (written in C, either Win or Linux)
FreeTTS (java, cross)
flite (written in C, once again from CMU)
Web version: At&t text-to-speech (not open licensed)