Redis

Redis (from: "REmote DIctionary Server") is a next-generation data structure server, exceptionally well-designed for building scalable and performance-sensitive web applications. Distinctive for its extremely high speed (able to perform over 82k GETs per second), support for rich data types, atomic operations and the multi-utility nature, the technology is used in a number of the world’s most massively visited web services and applications - Twitter, Pinterest, Flickr, GitHub, Digg, StackOverflow, and many others.