Deuce is an Emacs-like editor, for the Dylan programming language. It is a descendant of ZWEI, the Lisp Machine's Emacs, and made some interesting implementation decisions in representing the contents of its buffers, which made it easy to then make some powerful features, most notably composite buffers, which are pieced together fragments pulled in from different files, and changes in the composite buffer can then be pushed out to all the source files.
Some more details beyond the above link can be found in this comment [2] from comp.lang.dylan by Scott McKay, the original author of Deuce
[2] https://web.archive.org/web/20221002093520/https://groups.go...