Direnv has been mentioned, and it meshes well with functional package managers like Nix and Guix, each of which include the concept of "Profiles". Each profile

Direnv has been mentioned, and it meshes well with functional package managers like Nix and Guix, each of which include the concept of "Profiles". Each profile can access a specific set of programs via it's environment, but PATH is far from the last variable that you can use Direnv or Profiles to control.