Rexx study generally begins with http://www.rexxla.org
CL keeps a few pointers [L1 ]. Howard Fosdick nicely profiled [L2 ] its significance in the world of open source as of mid-2005, in light of IBM's release [L3 ] of Object Rexx.
Howard Fosdick profile is now at
A Tk binding for Rexx can be found at: http://rexxtk.sourceforge.net There have been others ...; this might be the most lively, as of 2004.