Open-source Implementations
One of the very first content-addressed storage servers, Venti, was originally developed for Plan 9 from Bell Labs and is now also available for Unix-like systems as part of Plan 9 from User Space.
A first step towards an open source CAS+ implementation is Twisted Storage.
Tahoe Least-Authority Filesystem is an open source implementation of CAS.
While it is generally used as a source code control system, Linus Torvalds' Git program is a userspace CAS filesystem.
Project Honeycomb is an open source API for CAS systems.
The XAM interface being developed under the auspices of the Storage Networking Industry Association is an attempt to create a standard interface for archiving on CAS (and CAS like) products and projects.
Bitcache is an open source distributed implementation of CAS written in Ruby. Bitcache server has an implementation for Drupal as well.
Camlistore is a recent project to bring the advantages of content-addressable storage "to the masses". It is intended to be used for a wide variety of use cases, including distributed backup; a snapshotted-by-default, version-controlled filesystem; and decentralised, permission-controlled filesharing.
Read more about this topic: Content-addressable Storage