Acapela 

InfoVoxis the voice that makes your computer speak and your life easier. Infovox is an open SAPI text-to-speech engine that lets you access your computer through your favourite screen reader, screen magnifier or any other application supporting speech. 

It can read any text you select, spell it for you while typing in any Windows application, let you access your computer through a screen reader and give a voice to any other application supporting voice output.

Infovox offers you a wide range of languages with a large selection of female and male voices with a smooth and natural pitch. A choice of voice packages including all voices of a language and multilingual packages for particular needs are available. The American English PRO voice Heather is provided for free as a bonus voice in each voice package.