Shell scripting. (I use `mksh`, slowly thinking of transitioning to `zsh`.) I find myself being able to do a huge fraction of my tasks with just shell, common Unix tools, and some very useful new command line tools (ex `jq`, `curl`, etc). I make heavy use of running `$EDITOR` (ex `vim` or `kakoune`) on a temp file for user interaction (ex selecting from SQL database into YAML, then using a tool that parses saved file and updates the DB).
But obviously you need a systems language for writing such lean, fast, reusable tools, and I think Nim or D are the best candidates.
