This is aXe. If you've never heard or seen aXe before, don't be shocked, it's hard to find online. (This repository has the easiest-to-obtain source code on the internet). aXe stands for "An X Editor", and it definitely is that.
aXe is very old. It uses X11 with Athena Widgets, and I love that. It's compatible, spanning from X11R4 all the way to modern XLibre systems (like mine). aXe was created by Jim Wight of the Department of Computing Science at the University of Newcastle in the United Kingdom sometime in 1992, origninally developed on Sun Microsystems SPARCstations with SunOS. aXe went through 2 years of development before it got stopped getting worked on.
There does not seem to be that much information about Mr. Wight online. There was a really famous person with the same name as him, and there was a guy that once went to the same university that Mr. Wight works/ed at. Mr. Wight doesn't have any websites or online accounts of any nature, and the only things online about him are probably decades-old university information about him. I don't know if he's dead or alive, or if he's retired or not, or if he's still using Unix/Linux to this day. But I think that's a good thing. He's probably in his 50-60's nowadays, and I hope he's doing well out there in the world these days.
You can find an archived version of 6.1.2 under the "original" branch (this is the "main") branch.
I don't plan to do any giant to the editor. Run tatr ls to see all the things needing to be changed. I might add more as I go on.