Nix and Guix are purely functional package managers, meaning that software builds are treated like a mathematical function: Input the same source code + dependencies and receive the same build as output. They have features such as reproducibile (often bit identical) builds, transactional package upgrades and rollbacks, and unprivileged package management. They solve the dynamic linking problem by allowing each package to refer precisely to the dependencies that it was built with. With this mechanism in place, it becomes very easy to use applications that require different versions of some C library, or a different Ruby/Python interpreter, or whatever else. Furthermore, it can do this without relying on a specific type of file system, and without requiring that applications be run inside containers or virtual machines. This makes it very composable and general-purpose.

https://nixos.org/

http://www.gnu.org/software/guix/