LessTif

For a long time motif has been the de-facto standard widget set in the professional world. This had one major issue, and that being that the source of motif was not free. We, the Hungry Programmers implemented a replacement called lesstif under a free license to provide a way to use free programs written for the motif widgetset. In 2012, the motif source has been relicensed to LGPL, making the lesstif source redundant and obsolete, as its goal has been achieved, a free motif. As lesstif is practically unmaintained and has serious bugs in the copy/paste realm, I advice to use the Motif source instead of this source.

LessTif is a free (LGPL) clone of Motif (also known as OSF/Motif). It is a set of widgets for developing graphical user interfaces. Motif is the most widespread such widget set, supported by most commercial UNIX vendors. LessTif is a free alternative.