MongoDB

MongoDB is a document orientated database that is part of the NoSQL movement and that allows for document storage in BSON format (a binary form of JSON).

It is upgradable in decentralised environments via replication and sharding mechanisms. Its particularly successful integration with most programming languages and its quality documentation have earned MongoDB its great popularity. MongoDB takes advantage of the sharp upturn in interest for document databases that are better aligned with modern environments that need to handle extremely heterogeneous data and for which relational DBMSs are not necessarily the most appropriate. It should be noted that many open source projects tend to integrate MongoDB for use as a storage engine. These include eZ Publish (which plans to use a NoSQL engine in its next major release) and Doctrine ODM (which applies the very popular ORM logic to a MongoDB database). Smile has already successfully integrated MongoDB with Magento to simplify the storage and handling of large volume catalogues.
Further, the database is supported by a commercial entity, 10gen, Inc. MongoDB is distributed under the Affero GPL.
It is written in C++.