Kagamine Rin & Len
Released on December 27, 2007, Rin & Len Kagamine (鏡音リン・レン, Kagamine Rin/Len) is the second installment of the Vocaloid Character Vocal Series developed by Crypton Future Media Ltd. (CFM), male voice (Len) and female voice (Rin). At first, CFM projected a Vocaloid with low-teen girl's voice following Miku Hatsune, but there was a demand for a boy's, so CFM adopted a voice actress who can produce both sounds. The developer says that their family name was from the developing code combining Kagami (鏡, mirror) and Ne (音, sound), i.e., they are the mirror reflections meaning Rin "right" and Len "left." This is, however, NOT an official announcement of CFM. Also CFM had an intension to distribute them as twins, this idea was not adopted, either. Still CFM seems to have no objection to this prevailing knowledge. According to Crypton's official blog, the package includes two voice banks: one for Rin and another for Len, both provided by the seiyū Asami Shimoda (下田 麻美).Despite the double voice banks, the package still sells at the same price as Miku Hatsune.
On June 12, 2008, Crypton announced the updated edition, named "act2", would be released in early July 2008. Users who had bought the old version got an expansion disc free of charge. On June 18, 2008, beta demonstration songs using the new version were released on the company's official blog.
The act.2 version is an independent installation, and coexists with the initial software.
via Wikia - Rin/Len Kagamine