For Rexx information, the best source would probably be the Rexx Home Page. IBM Object Rexx has gone open source, so if you want binaries or source code, download it from sourceforge. You can obtain Regina Rexx for Windows from the Regina Rexx home page http://regina-rexx.sourceforge.net/.
If you want to use the tags.x macro contained within xmacros.zip on the download page, you'll have to download the exuberant ctags program from Darren Hiebert's page.
Toby Thurston
has a fine collection of macros, and a document describing how to write
X2 macros. He's also got a nice package called XMail, which uses X2 as a base
for a simple POP mail client.
Some editors are discussed at the Softpanorama page.
Bruce Ediger has put together an extensive bibliography of
research papers dealing with editor design, user interface concepts, and
other research. If you're interested in a detailed description of (EMACS)
editor design, you may want to investigate The Craft of Text
Editing by Craig Finseth.
Roedy Green (I don't
know if that's his real name) has some interesting ideas about future editor
directions.
Dr. Dobbs Journal has a page that includes handy C++
programming information and links. This one's updated monthly.