Actually, Vocaloid isn't an anime! Nor does it have a plot! It's a computer program that toi can make songs with with voicebanks of certain prorgram thingys called "vocaloids". There are already thousands of songs made from the program :3 There are several vocaloid out there(like Miku Hatsune, LOLA, SeeU..) and there are 3 versions: Vocaloid 1, Vocaloid 2, and the most current one, Vocaloid 3. toi can buy one from one of these versions and there are vocaloid for other languages; there are English, Japanese, Korean, Chinese, Spanish, and a French one is coming up ^^ But toi can play around with the voices to make them sing different languages, but it may be hard(at least I think, haven't been around in this fandom for a few years) Hope it helped!
Vocaloid itself isn't an anime. Despite this, the vocaloid have appeared a few times in the fandom.
This is most récent to...not?
There is a song series sung par Miku and IA known as the Kagerou Project. This was made into a novel, the manga is in progress, and there is an animé that will be released this year.
Miku sung an ending for a 2013 anime, Watamote. It was the ending of the 6th episode.
In the OVA of Lucky Star, Kagami Hiiragi unintentionally wears a Miku outfit.
There are some other instances where Vocaloid is shown ou referenced to IN anime, but Vocaloid itself is not an anime.