Windows Animated Cursor

Overview
Windows Animated Cursor Format (ANI) is an animated image format, mostly used for cursors (mouse pointers) on Microsoft Windows.

Format
ANI files use the RIFF container format. Individual frames can be encoded in ICO format, CUR format, or a "raw pixel data" format that does not seem to be fully documented.

Resources

 * GFF Format Summary: Microsoft RIFF
 * Wikipedia article