Reason for being non-free: "This software is subject to an open license. It may only be used on, with or for operating systems which are themselves open source systems."

Open Group is going to release libmotif "under a license complying with the Open Source guidelines sometime in the future"

Resolution:
lesstif2-dev except that some software don't seem to work with it (e.g. those using Allegro Common Lisp Graphical Interface) (details)