mod_sivr_tts
Designed to work with ttsd | Manual
mod_yandex_tts
Yandex text-to-speech service | Manual
mod_google_tts
Google speech-to-text service (full featured, v1-api)
Opensource version and examples | Manual
mod_openai_tts
OpenAI text-to-speech service (full featured, v1-api)
Opensource version and examples | Manual
mod_piper_tts
A fast, local neural text to speech system ( rhasspy/piper )
Opensource version and examples | Manual

mod_sivr_tts | mod_yandex_tts | mod_google_tts | mod_openai_tts | mod_piper_tts

Feature	Commercial
Caching synthesis results	+
Configurable voices	+
Configurable language	+
Flexible HTTP settings (proxy/timeouts/etc...)	+
Source code	-
Price	$250

Feature	Opensource
Caching synthesis results	+
Configurable voices	+
Configurable language	+
Flexible HTTP settings (proxy/timeouts/etc...)	+
Source code	+

Feature	Opensource
Caching synthesis results	+
Configurable voices	+
Configurable language	+
Flexible HTTP settings (proxy/timeouts/etc...)	+
Source code	+