Redis key-value store server.

Redis is an advanced key-value store.

It is often referred to as a data structure server since keys can contain strings, hashes, lists, sets and sorted sets.

Written in ANSI C, it's open-source, networked, in-memory, persistent and  journaled. 

Supported languages or language bindings include C, C++, C#, Clojure, Common Lisp, Erlang, Haskell, Java, JavaScript, Lua, Objective-C, Perl, PHP, Python, R, Ruby, Scala, Go, and Tcl.
As of 15 March 2010, development of Redis is sponsored by VMware.

http://redis.io/
http://en.wikipedia.org/wiki/Redis (data store)
Redis: Lightweight key/value Store That Goes the Extra Mile
Evolving the Key/Value Programming Model to a Higher Level