In a word, fpTEX is a free port to Windows 9x and Windows NT– refered to as Win32 – of the well known distribution teTEX for Unix.
More precisely, given obvious differences between Unix and Win32, some things behave differently under fpTEX : some are still missing, some are just different, but the large majority behave just the same as under Unix. See section 1.4 for more details about the programs.