zmtx and zmrz impliement the ZMODEM error correcting protocol used to
send/receive files over a dial-in serial port.  And they do one thing
and only one thing -- transmit files.  They don't do file conversions,
they don't do remote commands, or any of that other stuff.

Note, zmtx-zmrx is not derived from Chuck Forsberg's rzsz package.  
The only restriction is that you will not use this software for
commercial purposes.  (commercial licenses are available contact the
author for info)