Attributed File System (AtFS)

 AtFS is a storage system supporting multiple versions of files and
 associating an arbitrary number of application defined attributes
 of the form "name=value" with each version. AtFS comes as a function
 library that is meant as an extension to the UNIX file system. It does
 this without the need for kernel modifications and without imposing any
 restrictions to existing file system applications. It is part of ShapeTools,
 a software configuration management system.