VOCALOID began from the simple concept of synthesizing the human vocals for singing. VOCALOID and its succeeding versions are voice synthesizing applications that have been sold commercially since 2004. And MOST IMPORTANTLY, now it's also available as VST (WIN) and AU (MAC). You can use the singing voice quickly and customize your own vocal.
VOCALOID5 has 4 voicebanks (Japanese/English), over 1000 vocal phrases and over 1000 audio samples.