GIFBLAST is a GIF "recompression" utility, and its associated .GFB file format. It was developed by Isaac Dimitrovsky.
It compresses a GIF image file to GFB format, which is usually smaller. The GFB file can later be decompressed back to a GIF file that is functionally identical to the original, though it will generally not be byte-for-byte identical.
GFB files apparently start with ASCII "
GB", followed by a byte for the format version number: 0x11 for v1.1, 0x20 for v2.0.