So, Vocaloid. What is it, how's it work, and why? Vocaloid is a singing snynthesis program made to imitate humans. It was developed by YAMAHA, but many companies have created different ones. Vocaloid engines, the software that allows the Vocaloid to sing was developed by YAMAHA. The companies use that engine to record human voices of every phenomen in whatever language it's designed for. The voice are called Voicebanks, and some have more than one installed. Kagamine Rin/Len so far have the most out f any other Vocaloid. Like many things, Vocaloid didn't start out al too great, with Vocaloid2 being better quality, "more human", than Vocaloid. Very recently, around September 2011, Vocaloid3 was created. This was by far the most realistic it's ever sounded. Some Vocaloids even get updates to thier software because of the advances. Like going from Pong to a 3DS.
The very first Vocaloid ever realesed was Leon, who was realesed in 2004. The most recent is Oliver on the Vocaloid3 engine, realsed December 21, 2011. At first Vocaloid wasn't really all too popular, not until a Japanese Vocaloid2 came out. Hatsune Miku, meaning Sound of the Future in English. It's believed that she is what started the Vocaloid fandom and it's heavy link to anime. There has been much merechandise sold, even a video game. Project Diva or PSP and one for the 3DS, both Asain contries only though.
The Vocaloid fandom is what caused Vocaloid to be so successfull. The songs were made by fans, for fans. Not a single thing is an "official" song. Everything, the artwork, music, videos, all made by fans. Some things are run by the companies though, mainly Crypton Future Media, who even had thier Hatsune Miku on a real rocket ship blasting into space. Hatsune Miku even had her own NASCAR, while other Crypton made Vocaloid were in concerts. Of course, they were only holograms.
You can find practically every song on Youtube or NicoNicoDouga, the Japanese Youtube.