Comparison of speech synthesizers

Here is a non-exhaustive comparison of speech synthesis programs:

General

Name	Creator(s)	First public release date	Latest stable version	Software license
15.ai	15	2020	2022
Apple PlainTalk	Apple Inc.	1984	2018	Bundled with Mac OS X
AT&T Natural Voices	AT&T Natural Voices	?	2008	Proprietary
Polly	Amazon AWS	2016	2019	Proprietary
Cepstral	Cepstral	2000	2013	Proprietary
CereProc	CereProc	2006	2017, February	Proprietary
eSpeak	Jonathan Duddington	2006, February 10	2022, April 3	GPLv3+
Festival Speech Synthesis System	CSTR	?	2014, December	MIT-like license
FreeTTS	Paul Lamere Philip Kwok Dirk Schnelle-Walka Willie Walker ...	2001, December 14	2009, March 9	BSD
LumenVox	LumenVox	2011	2019	Proprietary
Microsoft Speech API	Microsoft	1995	2012	Bundled with Windows
VoiceText	ReadSpeaker (Formerly Neospeech)	2002	2017	Proprietary
Nuance Vocalizer	Nuance Communications, Inc.	?	2018	Proprietary

Technical voice details

Platform	SSML	SAPI version	WS	PLS	CLI
15.ai	?	?	?	?	?
Apple PlainTalk	?	?	?	?	?
AT&T Natural Voices	Yes	5.1	?	?	?
Cepstral (company)	Yes	5.x	Yes	Yes	Yes
CereProc	Yes	5.x	Yes	Yes	Yes
eSpeak	Yes	5.x	?	?	Yes
Festival Speech Synthesis System	?	?	?	?	Yes
FreeTTS	?	?	?	?	?
LumenVox	Yes	5.x	Yes	Yes	Yes
Microsoft Speech API	5.x only	4.x/5.x	?	?	?
Nuance Vocalizer	?	?	?	?	?
VoiceText	Yes	5.x	?	?	?

Technical details

Name	Online demo	Available language(s)	Available voices	Programming language	Operating system(s)
15.ai	Yes	English (United States)	50+	Python	Any
Apple PlainTalk	?	English (United States), ...	15+	?	Macintosh
AT&T Natural Voices	Yes	English (British), English (Indian), English (US), French, French (Canadian), German, Italian, Spanish (Latin American)	20	C++	Linux Windows
Cepstral	Yes	English (British), English (US), Italian, French (Canadian), German, Spanish (American), ...	25+	C/C++	Mac OS X Windows i386-Linux x86-64-Linux Sparc-Solaris i386-Solaris
CereProc	Yes	English (British), English (US), English (Scottish), English (Irish), French, French (Canadian), German, Austrian German, Italian, Irish, Spanish (Castilian), Spanish (Latin American), Dutch, Polish, Portuguese, Portuguese (Brazilian), Japanese, Catalan, Scottish Gaelic, Swedish, Russian, Mandarin	46	Java / C C++ / Objective C / Python / C# & .Net through SAPI	Linux Windows Mac OS X Embedded Linux Android iOS Cloud service
eSpeak	Samples	Afrikaans, Albanian, Armenian, Cantonese, Catalan, Croatian, Czech, Danish, Dutch, English (British, US, Scottish, Westindies...), Esperanto, Estonian, Finnish, French (France, Belgium), Georgian, German, Greek, Hindi, Hungarian, Icelandic, Indonesian, Italian, Kannada, Kurdish, Latvian, Lojban, Macedonian, Malayalam, Mandarin, Norwegian, Persian, Polish, Portuguese, Romanian, Russian, Serbian, Slovak, Spanish, Swahili, Swedish, Tamil, Turkish, Vietnamese, Welsh.	several	C++	Linux Windows Mac OS X RISC OS
Festival Speech Synthesis System	Yes	English (UK), English (US), Spanish, Hindi, Croatian, Finnish, Polish, Welsh.	Several	C++	Linux Windows
FreeTTS	?	English...	Several	Java	Cross-platform
LumenVox	Yes	Danish, Dutch, English (Australian), English (US), English (UK), English (Welsh), English (Indian), French, French (Canadian), German, Icelandic, Italian, Polish, Portuguese, Portuguese (Brazilian), Romanian, Russian, Spanish (North American), Spanish (Latin American), Spanish (Castilian), Swedish, Turkish, Welsh, Welsh English	57	C/C++	Windows Linux
Nuance Vocalizer	Yes	US English, Australian English, Indian English, Irish English, South African English, UK English, Argentinian Spanish, Castilian Spanish, Colombian Spanish, Mexican Spanish, Arabic, Catalan, Basque, Galician, Dutch, Belgian Dutch, Portuguese, Brazilian Portuguese, Bulgarian, French, Canadian French, Cantonese (Hong Kong), Mandarin, Mandarin Taiwanese, Czech, Danish, Finnish, German, Greek, Hebrew, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Norwegian, Polish, Romanian, Russian, Slovak, Swedish, Thai, Turkish	70+	C/C++	Windows Linux Android
VoiceText	Yes	English (US), English (British), American Spanish, Canadian French, Chinese Mandarin, Japanese, Korean	13	C/C++/Java	Windows Linux