The original author was Andrew Wason of Bellcore (up to version 3.8). Release 4.0 was made by Kevin Brannen, maintenance from then until release 4.7 was in the hands of Andrew Lister (firstname.lastname@example.org). In the 4.7 release (July 1999), Andrew indicated that he wanted to transfer maintainership to someone else. As of then, Xbae is part of the LessTif distributions.
The Xbae Matrix widget has its own homepage on xbae.sf.net.