Here is an excerpt from the fedora-commons-users announcement:
At a glance, DOPs is a framework for the effective management and manipulation of diverse and heterogeneous digital material, providing repository-independent, type-consistent abstractions of stored digital objects. In DOPs, individual objects are treated as instances of their prototype and, hence, conform to its specifications automatically, regardless of the underlying storage format used to store and encode the objects.
The framework also provides inherent support for collections /sub-collections hierarchies and compound objects, while it allows DL-pertinent services to compose type-specific object behavior effectively. A DO Storage module is also available, which allows one to use the framework atop Fedora (thoroughly tested with Fedora version 2.0).