Below this paragraph lies a list of, in my opinion, useful software and other stuff. Useful doesn't mean it's simple but most programs here probably are simple enough to be considered, well, simple.

• Mate - simple C build system as a single-file library.
• kitty - fast, cute and very good GPU-based terminal emulator.
• cobalt.tools - useful social media content downloader without any ads or paywalls.
• Ventoy - useful, good, hackable bootable USB drive. Basically GRUB on a stick.
• Neovim - do I have to explain why it's on this list?
• Erlang and Elixir - The Erlang VM (BEAM) is a very good virtual machine. It's whole ecosystem, mainly OTP is great as well. I included Elixir because it's good too, it sits on top of Erlang and you can call Erlang code from it.
• librespot - maintainers are doing amazing work, which should be done by Spotify. But of course Spotify is a huge company and they won't give devs documentation for, mainly, Spotify Connect and ways to authenticate.