@nix-community is a GitHub organization that works alongside the @NixOS organization.
The @NixOS organization holds all the mission-critical projects such as Nix, Nixpkgs, NixOps, Hydra, etc.
The @nix-community organization is the community playground. We don't need to be as strict with permissions. The org can host any projects that benefit from a shared ownership. We provide infrastructure and support for those projects as well as visibility.