Multiple-image Network Graphics
Multiple-image Network Graphics (MNG) is a graphics file format, published in 2001, for animated images. Its specification is publicly documented and there are free software reference implementations available.
MNG is closely related to the PNG image format. When PNG development started in early 1995, developers decided not to incorporate support for animation, because the majority of the PNG developers felt that overloading a single file type with both still and animation features is a bad design, both for users (who have no simple way of determining to which class a given image file belongs) and for web servers (which should use a MIME type starting with image/ for stills and video/ for animations—GIF notwithstanding). However, work soon started on MNG as an animation-supporting version of PNG. Version 1.0 of the MNG specification was released on 31 January 2001.