Motif(r) is the industry standard graphical user interface, (as defined by
the IEEE 1295 specification), used on more than 200 hardware and software
platforms.  It provides application developers, end users, and system
vendors with the industry's most widely used environment for standardizing
application presentation on a wide range of platforms.  Motif is the
leading user interface toolkit for the UNIX(r) system.

Here is what you might ask.  (excerpted from The Open Group FAQ)

  Q:  What is Open Motif? How does it differ from standard Motif?

  A:  Aside from some different copyright and license statements, both
  Motif and Open Motif share the same functionality and source code.  The
  primary difference is the software license for each of the software
  products. Open Motif source code and binaries can be distributed royalty
  free under The Open Group Public License as long as the operating system
  upon which Open Motif is running meets the OSI's Open Source Definition.
  Motif is made available under the standard Open Group software licenses
  and requires the payment of source code and royalty fees.
  
Visit http://www.motifzone.org for more information about Motif.

NOTE: Some ports with GNU configure do not know that Motif 2.1 requires -lXp.
In that case, you need to edit Makefile after configure, or, hack
configure(.in) before configure.

WWW: http://www.opengroup.org/openmotif/