Comment by drakerossman

It (obviously) leverages Nix, which in turn means the environment is declarative and fully reproducible (not "reproducible" as in docker). Now, you can use just Nix's devShells, but with devenv you have a middleground between just Nix package manager and a full fledged NixOS module system. Basically, write out one line of code - and you've got your Postgres, another one - full linter set up for whatever language you're using, etc.