No, it builds on top of nix. But it seems like the only real option for declarative package management.
Nix shell and nix-shell are different commands
https://discourse.nixos.org/t/nix-shell-nix-shell-and-nix-develop/25964/4
Nix run iirc only works with flakes
So does nix shell
https://discourse.nixos.org/t/nix-shell-nix-shell-and-nix-develop/25964/4