I'd like announce a little project I've been working on lately. It called Bocas and it is a Java and REST API to access key-value repositories with the content-addressed storage constraint, that is, the key must be a hash of the value. In the current implementation, SHA-256 is used as the hash function.
A few releases have been already deployed in Maven Central, and documentation is being built at the project web site. As this site is still short of content, you may find the API documentation useful, above all the main API interface.
The project is hosted on Google Code and has the Apache 2 license.
Stay tuned for more news about this project.