I can vouch for the immense improvement Nix has made to my software development process. I use NixOS on my desktop and laptop. At the OS-level, it gets a lot of things right: reproducible, immutable system configs; lightweight containers; devops with declarative configs. At a software project level, nix-shell is an indispensible tool. Compilers and interpreters aren't even part of my system-wide config; instead each…
By reading your comment and a little bit of the package declarations in some nix packages, it seems like the software package system of nix is very similar to rez. Rez ( https://github.com/nerdvegas/rez ) is used by some visual effects companies (including mine) to manage software packages. It allows us to have great flexibility in the mix & match of software versions and runtime environments.
For Nix, this is almost a side-effect, however. Nix's primary task is to describe how to build packages, and the entire OS is just another package that groups all dependencies. You can make a single change to a file everything depends on and it will result in a new OS.
Nix can evaluate the entire system configuration in seconds, and build or download missing binaries in parallel.
As a result you can e.g. have a complete OS based on a different glibc (maybe with some patch you like) installed and running alongside the normal OS without the glibc patch. Packages that do not use glibc are simply shared.