Emacs
A text editor… but also way more.
Jujutsu
A VCS with a better (Mercurial-like) paradigm
Zellij
A batteries-included Tmux
Fish
A batteries-included, low-setup shell
Guix
A less-supported Nix but in Scheme and with better documentation and (in my opinion) more coherent and considerate design decisions

Honorable mentions §

Syncthing
Sync files across devices
Zoxide
A cd with memory
Astro
A pain-free “framework” that whose specialty is generating small bundles and static pages; used to build this site