MikuMikuDance is a piece of 3D animation software created for making Hatsune Miku, the popular Vocaloid mascot, dance. The software is actually freeware, and is being published via Steam in English by Sekai Project. (Thanks, Anime News Network)
MikuMikuDance allows users to upload and animate 3D models, and use them to create videos. It was submitted to Steam via Steam Greenlight, and was recently greenlit for release. A release date has not been announced, but you can access its Steam page here.