It's a Japanese site developed by Vocaloid fans to help keep track of all Vocaloid-related events happening in Japan. Not only that, the sites also updates frequently about figurine release dates, CD release dates, special TV broadcast, NND special broadcasts and many more.
A simple click on the event title and a pop up will appear, providing details of the event and the related external sites. Also, you can view VOCALENDAR using smartphones too.
Currently, the site is only available in Japanese language and it is still in Beta phase.