Since I didn't know:

"Riak is a Dynamo-inspired key/value store that scales predictably and easily. Riak also simplifies development by giving developers the ability to quickly prototype, test, and deploy their applications

A truly fault-tolerant system, Riak has no single point of failure. No machines are special or central in Riak, so developers and operations professionals can decide exactly how fault-tolerant they want and need their applications to be."