Guix is a tool for declarative and reproducible software deployment. You can view it as a package manager, but it's also an OS configuration management tool, a container image provisioning tool, and more.
Guix 1.0 was released just two months ago. The announcement summarizes what it can do for you in these areas: https://guix.gnu.org/blog/2019/gnu-guix-1.0.0-released/ .