NixOS is a GNU/Linux distribution based on declarative builds using the functional Nix package manager. It boasts the most amount of available software on any Linux distribution as well as configuration options for various programs. There are more than 100,000 packages on nixpkgs as well as more than 10,000 options for system configuration.

Nix resources:

• Vimjoyer's video series on Nix hosted on YouTube (invidious proxy)
• No Boilerplate on NixOS (invidious proxy)

NixOS is a great way to learn how GNU/Linux works as well as to build a system configuration that you can take anywhere, anytime.