nix-rage is age/rage based tool designed to manage of encrypted configuration files within the Nix ecosystem. Unlike agenix or sops-nix, this tool is not designed for the secure use of passwords, tokens, etc. It is designed to hide personal information in public repositories. If you want to share your fancy nix config, but do not want to disclose your home address or your "secret" email, then this is the tool for you.
The nix-rage package is currently in an unstable development phase and is not recommended for use in sensitive configurations.