http://www.crypton.co.jp/mp/pages/prod/ ... d/cv01.jsp
It is a software called "hatsune miku" ,use the engine of yamaha's "VOCALOID 2"
You can input the melody and lyrics to produce a song(Japanese only^_^; ,of course you can input English,but it just like a Japanese speak English)
Let listen to the sample in youtube,is Maaya's 約束はいらない
http://www.youtube.com/watch?v=NBbGeh9wZmc