NixOS
NixOS is a Linux distribution with a unique approach to package and configuration management. Built on top of the Nix package manager, it is completely declarative, makes upgrading systems reliable, and has many other advantages.
I have been using NixOS as my Linux distro of choice since November 2019.
Home Manager
Home Manager is a project that allows you to manage your user environment using Nix, much like how you manage your system's global configuration. This is preferable, as it means that multiple users on the machine can have control over their own environments. In my case, I am the only user on my machine, but I still use Home Manager as it means I don't need root privileges to install new packages.
Binaries
Downloading and attempting to run a binary on NixOS will almost never work. This is due to hard-coded paths in the executable.
This is one thing to keep in mind when running NixOS. Just today I tried to run a binary off GitHub and was confused when it didn't work.