a graphical user interface toolkit used in software development
Motif is one of the first X toolkits, a sucessor of the Athena Widgets (Xaw).
Some resources include:
The Motif Programming Manual, by Dan Heller and Paula Ferguson. Also on O'Reilly.
Open Motif documentation in the The Open Group website.
motifdeveloper.com bulletin board.
Kenton Lee X and Motif consulting (on WebArchive).
Compilation of frequently asked questions (Kenton Lee's version on WebArchive).
Dave Marshall's lecture notes, a step by step approach.
Open-source packages tagged with Motif in Debian repositories (see also Xmgrace).