* APL -- I haven't dedicated the time to learning in part because there's little support where I normally work. I'd love for APL to have be adapted like a domain specific language a la perl compatible regular expressions for various languages (april in common lisp, APL.jl in julia).
* regular expressions. https://xkcd.com/1171/
* bugs/issue tracking embedded in git https://github.com/MichaelMure/git-bug/
But I'm more excited for things that fall into the niche/lesser-known side of of unpopular. I love finding the little gems that change how I organize or work with the system. * "type efficiently by saying syllables and literal words" https://sr.ht/~geb/numen/
* I use fasd[0] 'z' alias for jumping to previous directories in shell every day.
* Alt+. in shell (readline, bash) to get the previous commands last argument is another ergonomic time saver that I think is relatively obscure. I have a bash wrapper to combine that with fzf for quick any-previous-command-argument fuzzy search and insert [1]
* zimwiki [2] (and/or a less capable emacs mode[3]) for note taking has served me well for a decade+
* DokuWiki's XML RPC [4] enables local editor edits to a web wiki. I wish it was picked up by more editor plugin developers. (cf. emacs-dokiwki [5])
* xterm isn't unpopular per say, but I don't see sixel support and title setting escape codes talked about often. I depend on a bash debug trap to update the prompt with escape codes that set the terminal title [6]
* are clipboard managers popular? I get a lot out of using https://github.com/erebe/greenclip[0] https://github.com/clvv/fasd [1] https://github.com/WillForan/fuzzy_arg [2] https://zim-wiki.org/ [3] https://github.com/WillForan/zim-wiki-mode [4] https://www.dokuwiki.org/xmlrpc [5] https://github.com/flexibeast/emacs-dokuwiki [6] https://github.com/WillForan/dotconf/blob/master/bash/PS1.ba... -- bash debug trap to update prompt with escape codes that set the title to previous run command -- to eg. search windows for the terminal playing music from 'mpv'