The original commenter called magicpak a 'cool alternative to nix', to which I replied that nix is an industrial-strength, tested and very through solution, while magicpak is more like a dirty hack. (We used to have an internal tool much like magicpak before nix came along.)
But I guess it's useful if you already have an ad-hoc build system and you can't/won't migrate to something industrial-strength.