Nix-on-Droid brings Nix package manager of NixOS fame to your mobile device. If you're not after its advanced features, you might still be interested in tapping into nixpkgs, a vast collection of precompiled software.
At first start the app will download Nix repackaged for Android, leaving you with a barebones system afterwards. If you are an experienced Nix user, you know what to do next. If you are in doubt, follow the on-screen instructions, to install more of the familiar Linux software and declaratively manage your environment.
NOTE: this software is alpha-quality. Users that value stability and Android integration over features and package selection might better be served with Termux as of now.
Nix-on-Droid uses a fork of Termux application as a terminal emulator.