Windows Font Library (.fon)
The FON file extension, part of the Windows Font Library, refers to a font library file used in Microsoft Windows 3.x. It is essentially an executable file renamed to FON, containing a collection of FNT files, which are bitmapped or stroked fonts. These files were used by applications to access system fonts. However, FON files are now obsolete, having been replaced by TrueType and OpenType fonts due to their limitations, such as the inability to resize fonts. The Microsoft Windows Font Viewer can open FON files.