“Alter/Ego is based on the award winning technology featured in chipspeech but instead of targeting Vintage voice technology, it focuses on more ‘modern’ (1990+) singing synthesis algorithms and research.
It is specially tailored for musical needs – simply type in your lyrics, and then play on your MIDI keyboard. It’s a true synthesizer, the sound can be extensively modified for easy and expressive performances.
And more importantly it is FREE!”
Source & LINK : http://www.plogue.com/products/alterego/