TTS+ is a plugin for FBReader on Android, a product of geometerplus.
You can find FBReader in Google Play Store, and the source code to
it as https://github.com/geometer/FBReaderJ. TTS+ Plugin is a free
product, licensed under Apache License 2.0.

The TTS+ plugin works relatively well with FBReader 1.5.x currently
released, but to work really well it would need some changes to
FBReader, which I suggested to the author of the reader. You may also
find a fork of FBReaderJ project on GitHub with these changes implemented,
and it's build as .apk file is available on our web site (address below).

Greg Kochaniak
Hyperionics Technology LLC
http://www.hyperionics.com/?Page=/TtsPlus