What is "mikumikudance"

MikuMikuDance, commonly abbreviated to MMD, is a freeware animation program that lets users animate and create 3D animation movies, originally produced for the Vocaloid character Hatsune Miku. The MikuMikuDance program itself was programmed by Yu Higuchi (HiguchiM) and has gone through significant upgrades since its creation. Its production was made as part of the VOCALOID Promotion Video Project (VPVP).