I personally love using https://taskwarrior.org/ to manage my TODO-lists and quick notes. Since alot of my work is done in the terminal anyways, it is nice to also have a little command line decorator telling me about remaining + urgent tasks.
Also a lot leaner than e.g. GNOME Notes with much more functionality under the hood (e.g. it can also display a calendar with upcoming tasks)
Some of my favourite command line tools, of the top of my head (there are countless more):
ffmpeg – video editing imagemagick – picture editing pdftk – PDF editing svgo, svgcleaner – SVG optimisers youtube-dl, yt-dlp – download YouTube videos (the main way I use YouTube) wget – download anything from the CLI
Of course, there are countless compilers and assemblers, desktop publishing systems like LATEX, text editing utilities like sed, awk, but most people know about these…
I currently only use one CLI tool and its a simple task/todo manager. I wanted to start easy and not with a crazy learning curve, so I chose Ultralist. I absolutely love it. Made a few alias’ as well to slim down my keystrokes.