What Is TTS?

From Wikipedia, TTS (Text To Speech) is defined as follows:

"Speech synthesis (Text to speech) is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware. A text-to-speech (TTS) system converts normal language text into speech; other systems render symbolic linguistic representations like phonetic transcriptions into speech."

TTS Software

Asterisk flite: Can replace Festival in Asterisk
asterisk-agi-audiotx: Asterisk AGI extension module that adds commands to allow the transfer of audio files to and from Asterisk via an AGI session
asterisk-espeak: Asterisk dialplan application providing speech synthesis using the eSpeak text-to-speech engine
Database Systems Corp. CTI technology with text to speech converter for IVR and voice broadcast applications.
Festival

Acapela Voices - including Arabic, Czech, Danish, Dutch (NL), Dutch (B), English (UK), English (US), Faroe, French, Finnish, German, Greek, Icelandic, Italian, Norwegian, Polish, Portuguese, Portuguese (Brazil), Russian, Spanish, Spanish (South America), Swedish and Turkish
AT&T Labs Text-to-Speech - TTS including German, French, Latin Am. Spanish
cepstral Medium quality, low-cost voices
ELAN SaySo - including German, French, Spanish and Italian voices/phonems
Loquendo TTS
Mbrola - a Freely Available Multilingual Speech Synthesizer for many languages
Nuance Realspeak - supports 24 languages and dialects and more than 30 voices
Sakrament TTS Engine - including Russian, with English coming soon
Verbose Text - can use any SAPI4 or SAPI5 voice