chrpath is a command line tool to adjust the RPATH or RUNPATH of ELF binaries. (Yes, it is similar to our patchelf tool.) gpsd and Yocto/OpenEmbedded depend on chrpath (although we have currently patched that dependency out of gpsd).
Nixpkgs is a collection of packages for Nix package manager. Nixpkgs also includes NixOS linux distribution source code.