There is only one file type that uses the .NEO extension:
NeoChrome Bitmap Image
Raster graphic created by NeoChrome, an early image-editing program used by the Atari ST and TT systems; supports color images and animated frames; can still be opened in some image viewing and conversion programs.
The Atari ST and TT computer families were discontinued in the early 1990s.
Updated: September 30, 2015