Fief is a user-space, cross-platform, branched (multi-versioned), asynchronous, package manager for scientific computing currently under development. It aims to address the issues of total or partial stack reproducibility while providing a consistent interface across posix, Windows, Mac OSX (darwin), and HPC systems. Both source and binary packages are handled easily in the fief model. As with many package managers, fief is written primarily in Python. Fief was conceived of by Anthony Scopatz and co-implemented with John Bachan on top of John's bake and async technologies.