This is a sort of nostalgic post and, in some sense, it is also a "toot your own horn" one as well. I am writing this mainly for myself. I am trying to remind myself what I've liked most about programming.
Years ago, actually almost 2 decades ago -- around 1996, I wrote a text mark up system called AFT. AFT stood for Almost Free Text. It was inspired by Ward Cunningham's original Wiki mark up but went further.
I had a problem. I didn't like using WYSIWYG word processors and the world was moving towards HTML. I liked Ward's mark up. He was using it on this new "Wiki Wiki" thing. I answered an invite sent to the Patterns List and became one of the first of the wiki users in 1995. (But that is a different story or a different time.)
AFT was my attempt at a writing system to produce publishable (web and print) documentation. Since then, it has developed a (now waning) user base. You can see how many web pages/documents use it without changing the default "watermark" with this query.
As of Ubuntu 14.04, you can get AFT by issuing an "apt-get install aft" against the standard repository.
I think it is still part of FreeBSD "world". I believe it still runs under Windows too.
Various "modern" mark up languages (written in "modern" programming languages) have since surpassed AFT in adoption, but for me, it still is a more elegant and pleasurable experience.
Over the years (although not very recently), I've updated, fixed and generally maintained the code. There are no known crashes (it literally take whatever you throw at it and tries to produce good looking output -- although that may fail) and it doesn't require me to look at the HTML (or PDF) manual (written in AFT!) unless I want to do something complex.
AFT is implemented in Perl. Originally it was written in awk, but I taught myself Perl so as to re-implement it in the late 1990s.
It is, for me, interesting Perl code. I have modernized it over the years, but it still doesn't depend on CPAN (a good thing if you just want to have non-programmers "download it" and run without dependencies -- yes I know there are packaging solutions to that problem today...).
AFT has "back end" support for HTML, LaTeX, lout and some rudimentary RTF. These days I think mostly HTML and LaTeX is used.
You can customize the HTML or LaTeX to support different styles by modifying or creating a configuration file. This configuration file is "compiled" into a Perl module and becomes part of the run time script.
AFT has been a pleasure to hack on now and then. It still runs flawlessly on new Perl releases and has proven not too fragile to add experimental features to. I've accepted some small code fixes and fragments over the years, but generally it is mostly my code.
As I wrote (and rewrote) AFT, I thought frequently of Don Knuth's coding approach (as excellently documenting in my all time favorite book on programming: Literate Programming). I certainly can't match the master, but the slow thoughtful development he enthuses was inspiring.
Over the years I've gotten a few "thank you" notes for AFT (but nothing in the past few years) and that makes it my (to date) proudest contribution to Free Software.
Maybe I'll dust off the code and introduce some more experimental features...