flake-compat is a compatibility shim for the Nix package manager that enables the use of Nix flakes—a dependency management feature—on older or alternative versions of Nix that lack native flake support, including stable Nix releases and versions prior to 2.4. Built in Nix, the project provides functions that fetch flake inputs and invoke the flake's outputs function, returning attributes like `defaultNix`, `shellNix`, and `outputs` for integration with existing Nix workflows. Originally created by Eelco Dolstra, flake-compat is now maintained by the NixOS community under the NixOS organization.