Rhetorical Systems is a company that develops text-to-speech
products, mostly for the IVR
(interactive voice response) mark.
The company is based in Scotland. Its flaghsip product is rVoice.
rVoice is probably the best TTS out there. It produces amazingly lifelike voices in a huge number of accents, from Australian Female, to Old Scottish Male, to Valley Girl, with amazing fidelity. Sometimes you really can't believe it's synthesised, it sounds so real.
rVoice uses concatenative speech synthesis, rather than the more old-fashioned parametric speech synthesis techniques.
They can be found on the Web at: