It can be used like memcached, in front of a traditional database, or on its own thanks to the fact that the in-memory datasets are not volatile but instead persisted on disk. One of the cool features is that you can store not only strings, but lists and sets supporting atomic operations to push/pop elements.

The library includes multiple server support, content hashing, keys as objects and full Zend Framework integration. You can find out more about the project on its site or just download the latest version.