whats the best text to speech engine sdk?

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Javascript

Hi.
A blind person using the jaws for windows screen reader from http://www.freedomscientific.com, and enrolled in certificate eiv programming from http://www.upskilled.edu.au. Now doing a mobile application assignment for my mobile programming subject.
Doing a web based accessible mobile game space invaders. Now, looking for a good text to speech engine free, as do not have a credit card.
That has good sounding voices.
Any suggestions.
Will be using html 5, got a flash game tutorial, but will be adapting it for html 5, and got visual studio 2015 community edition 32 bit, and using windows 10 64 bit pro on a Toshiba satellite pro c-50-a.
Any ideas.
Marvin from Adelaide, Australia.,