Or if you really want to be that basic, just use any terxt editor, such as Microsoft's 'Notepad.
there's nothing magic about GEDCOM files. They are a seriesd of tagged rows of data typed in a simple text file.
Of course you do need to understand the underlying structure, but a read of the GEDCOM specification will provide that. Its not hard.
If thats too basic, then I see little benefit in doing anything other than getting software like FTM and using its data entry facilities, which are designed to avoid the need to understand the GEDCOM spec. Ignore all its 'bells and whistles' and it does just what you are looking for.