In comparison to other vocal synthesizers, Alter/Ego is less user-friendly, with most of the features sort-of hidden, and creates less realistic results. However, it has a unique sound that makes it worth trying out. Also, it's free. Just, remember to space out the notes to allow the pronunciation and phonemes to render correctly.
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!
Though you have to purchase additional voicebanks if you want anything other than the default, both the default voicebank (Bones) and the player are free and quite simple to use. It doesn't sound quite like a real person, but since it's not really intended for that it's quite all right. However, it can be a little difficult to get it to do what you want, as the timing of the vocal is a little off.