You do not need all of this.

Choose NixOS when you want the Linux system itself described through Nix: packages, services and system settings.

Choose Nix for tools, project environments and build definitions. It also works without NixOS.

Home Manager manages selected user packages and dotfiles. It can run separately or integrate with NixOS and nix-darwin. Begin with a small configuration and back up files you already manage by hand.

nix-darwin applies a Nix module-based approach to supported parts of macOS configuration. macOS remains the operating system.

A community project for running NixOS under Windows Subsystem for Linux, with installation and integration specific to that environment.

Access Nix tools from an Android app. This is a specialist, prototype-grade route rather than a replacement phone OS.

An experimental Nix-based OS built around finit. Read its own modules and installation guidance rather than assuming NixOS configuration is interchangeable.