Also known as: Iwara, Iwara.tv
Iwara.tv is a Japanese video hosting site. Originally dedicated to MMD videos, Iwara later covered various other 3D animation mediums, such as Blender (Medium), Koikatsu (Medium), Source Filmmaker (Medium), etc..
The NSFW version of the site (ecchi.iwara.tv) in particular has become popular and (in)famous in its own right due to its own distinct culture, particularly the usage of Sin Sack as the stock "stud" character in the videos.