If you haven't heard about vocaloid, vocaloid is a voice synthesizer program made by Crypton Future Media Inc., Yamaha, Sony and other companies that collabed to make Vocaloid.
It was made so machines can have its own natural voice generator.
Since its success, it has started producing digital pop stars like Miku, Len, Rin, etc that even performed on concerts.
It's not an anime, game, or anything else, it's its own thing.