Source released under the terms of the GNU GENERAL PUBLIC LICENSE. This was written in Borland Delphi 6 (should compile fine in Delphi 5). I've included the DirDlg component (required to build the GUI version), as the author's homepage is no longer functional.
mrtool_core.pas contains the bulk of the actual MR [en|de]coder. mrtool
is the Win32 command-line wrapper, mrtool_gui is the Win32 GUI wrapper.
Do with as you will, but remember, if you base something upon this, you must release source.