ChromeOS comes with a port of the open-source eSpeak-NG speech synthesis engine. eSpeak-NG is lower quality than Google‘s “PATTS” speech engine, but it’s faster, uses less resources, and supports more languages.
eSpeak-NG is an open-source project, released under the GPL v3 license. The current home of the project is on GitHub:
NG stands for Next Generation. It's a fork of the eSpeak engine created by Jonathan Duddington.
There are two reasons we include eSpeak-NG in ChromeOS:
The source code to the ChromeOS port of eSpeak-NG can be found in google3
The google3 repository automatically syncs its changes to the googlesource repository via copybara. All of the Chrome-specific changes are in the “chrome” branch.
For instructions for building, deploying, and releasing eSpeak-NG see the README in google3
See Chromevox on Desktop Linux for more how to use eSpeak's speech engine on ChromeOS emulated on desktop Linux.