NixOS
NixOS Wiki: Cheatsheet - a cheat sheet and rough mapping between Ubuntu and NixOS
Fluffy Nuke It: Installing Essential Software in NixOS - technically about setting up NixOS for Haskell development, but does a good job of walking through and explaining how things work.
For example, here’s how to install git:
nix-env -iA nixos.pkgs.gitAndTools.gitFull