Just Nix (+ home-manager) for now 
I’ve tried NixOS a few times and bounced off it; will probably give it another go once I understand the internals a bit better (or when the UX improves to the point that I don’t need to do that to get by).
It’s definitely a thing, though not quite as much as in the Haskell community (yet). We have opam2nix for building Nix development environments, and there are at least a few big projects that do this (coq and dune spring to mind). We also have a few people doing really cool things with e.g. Nix cross compilation, which go way above my head for now.