• Emacs is one of my primary tools. It's not just an editor, it has many use-cases and micro-applications within. But it's very hard and long-winded to get into. Not recommended for just checking it out. You need to be certain that that's a tool you want to use long-term.
• pass is a simple but amazing CLI-based password manager. It requires a gpg key pair (because it uses gpg for en-/decryption), which is a tool that's notoriously hard to get into, but once you've got that, pass is amazing, especially when paired with the script passmenu + the tool wofi/dmenu, as you'll have insanely fast access to any stored password on hotkey press.
• syncthing is a great way to sync files across devices (serverless, you just need a discovery host (self-hosted or public) for your devices to find each other over the internet). Easy to use.
• Some (usually rust-based) coreutils alternatives like exa (ls), bat (cat), fd (find), procs (ps) are nicer to use than the "originals"
• ripgrep (rg) - MUCH faster than grep. Recommendation: use smart case (meaning that if you type your search term in lower case, it searches case-insensitively (which is usually what you want), but as soon as you include at least 1 cap, it searches case-sensitively, which is smart)
• ripgrep-all (rga) - allows you to full-text-search through "everything" (including some binary formats like PDFs, Office documents, zips, ...). Insanely fast as well.
• ledger - is a plain-text accounting software for tracking and introspecting your finances or expenses in plain-text form (also has a great Emacs package/integration from the same author)
• fzf - can be combined with other tools or scripts to allow fuzzy-searching through various result lists. Here's a neat example from my bash aliases ("pi" stands for "package install", name it whatever) which you can use on an Arch-based distribution to have a fast fuzzy-search mini TUI package installer, it's just cool:

pi() { printf '\e[1;37m[pacman] \e[1;32mInstall new packages (TAB to select, ENTER to install)\e[0m'; pacman -Sl | awk '{print $2($4=="" ? "" : " *")}' | fzf --multi --reverse --info=inline --height='80%' --color='hl:148,hl+:154,pointer:032,marker:010,bg+:237,gutter:008' --prompt='> ' --pointer='▶' --marker='✓' --bind='?:toggle-preview' --bind='ctrl-a:select-all' --preview='pacman -Si {1}' | xargs -ro sudo pacman -S --needed; }