A next-generation package manager called Nix provides a simple distribution-independent method for deploying a binary or source package on different flavours of Linux. Even better, Nix does not interfere with existing package managers. Nix allows different versions of software to live side by side, and permits sane rollbacks of software upgrades. Nix is a useful system administration tool for heterogeneous environments and developers who write software supported on different libraries, compilers, or interpreters. Why provide yet another package manager? Because current package managers fall short in the upgrade cycle. Everyone gets burnt by software dependencies, at some point. In particular, with a major release of any given distribution, many people choose not to upgrade until it is time to do a fresh install. With Nix, upgrades are always safe: they don't overwrite previously installed packages. This means previous versions will continue to work, and you can easily roll back.