Is there a standalone Nixpkgs “standard library” to create private Nixpkgs repos?

Is there any project/repo that contains "standard library" functions extracted from the Nixpkgs repo?

Currently reading the Nixpkgs manual, and it seems that the Nixpkgs repo consists of

functions that actually help build (cross-platform) packages (written using the Nix builtin's/primitives)
collection of packages

Tried to find decentralization examples, but there aren't many (or I didn't find them). I like Cachix and the philosophy behind it, but that is for already built packages (unless I misunderstand something, which is more than possible).

Some of the resources found:

Managing private Nix packages outside the Nixpkgs tree [Sander van der Burg]
I create a local repository for NixOS/nixpkgs? [Unix/Linux Stack Exchange]

EDIT: Just found out about Nix User Repository (NUR).

EDIT2: Here's the thread on NixOS discourse.

Solution

Nixpkgs is a "megarepo", bundling highly related Nix projects, such as Nixpkgs, its standard library, NixOS and such. I am not aware of any other source or 'mirror' of these projects. If you want this to change, you can help out with the Nix Flakes idea/project/projects.

Today, if you only really need pkgs.lib, you can use lib = import <nixpkgs/lib>.