Nixpkgs: The big recipe book of open source

I have seen a lot of Nix threads on HN recently, awesome. I'm not using NixOS as my main OS, but I have set up a VM and am trying to contribute. I'm fairly certain that the biggest hurdles to Nix packaging are all the language package managers for languages like Haskell, Ruby, Python and NodeJS.

Does anyone know of a decent GUI for managing settings/packages for NixOS?