Riak is a NoSQL database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

 implementing the principles from Amazon's Dynamo

Dynamo (storage system)

Dynamo is a highly available, proprietary key-value structured storage system or a distributed data store. It has properties of both databases and distributed hash tables...

 paper.

Riak has a pluggable backend for its core shard-partitioned

Shard (database architecture)

A database shard is a horizontal partition in a database or search engine. Each individual partition is referred to as a shard or database shard.- Database architecture :...

 storage, with the default storage backend being Bitcask as of the 0.12 release. Riak also has built-in MapReduce

MapReduce

MapReduce is a software framework introduced by Google in 2004 to support distributed computing on large data sets on clusters of computers. Parts of the framework are patented in some countries....

 with native support for both JavaScript

JavaScript

JavaScript is a prototype-based scripting language that is dynamic, weakly typed and has first-class functions. It is a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles....

 (using the SpiderMonkey

SpiderMonkey

SpiderMonkey is the code name for the first-ever JavaScript engine, written by Brendan Eich at Netscape Communications, later released as open source and now maintained by the Mozilla Foundation.-History:Eich "wrote JavaScript in ten days" in 1995,...

 runtime) and Erlang, while supporting a variety of additional language drivers such as Python

Python (programming language)

Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...

, Java

Java

Java is an island of Indonesia. With a population of 135 million , it is the world's most populous island, and one of the most densely populated regions in the world. It is home to 60% of Indonesia's population. The Indonesian capital city, Jakarta, is in west Java...

, PHP

PHP

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

 and Ruby

Ruby (programming language)

Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto...

.

Current production Riak users include Voxer, Comcast, Mozilla, AOL, Ask.com, Yammer, Mobile Interactive Group, Wikia, Opscode, and Mochi Media.