In 1990, I was using the BRIEF editor on MS-DOS, which was an editor for programmers and which was quite similar to Emacs (also including a scripting language somewhat similar to LISP). BRIEF must have already existed for some years.

It had a completely configurable auto-complete, which I rewrote to insert big code templates in the languages that I was using (C, C++, Fortran, Basic, assembly), covering almost all boilerplate that I encountered at that time.

The BRIEF editor for programmers was one of the best software products that I have ever used. Nothing that I encountered later on Windows approached it in customizability. Actually I find it strange that I cannot recall any Windows program that I would consider as a high-quality software product, while there are a handful of programs for MS-DOS that I consider as examples of high-quality, even decades later (e.g. the programming editor BRIEF, the file manager XTree, the spreadsheet Lotus 1-2-3, the technical drawing program AutoCAD for MS-DOS; all these were extremely customizable).

Nowadays Emacs may have even more customizable features, but it has always been more opaque for newbies. BRIEF was instantly usable on an IBM PC clone, even if discovering its advanced features could require some time.

Despite having used continuously for 3 decades various UNIX-derived operating systems, including Solaris, FreeBSD and Linux, only this year I have switched to Emacs, in order to recreate the great programming experience that I had with BRIEF many years ago. Emacs includes all that is necessary, but it requires a much longer initial study in comparison with BRIEF, before becoming able to master it, which is why I hesitated for a long time before trying it.