CouchDB

CouchDB is an open source NoSQL database based on common standards to facilitate Web accessibility and compatibility with a variety of devices.

NoSQL databases are useful for very large sets of distributed data, especially for the large amounts of non-uniform data in various formats that is characteristic of big data. Data in CouchDB is stored in the JavaScript object notification (JSON) format, and organized as key-value pairs. The key is a unique identifier of the data and the value is the data itself or a pointer to the data’s location. Standard database functions are all performed by JavaScript. OS-agnostic, device-independent Web standards allow databases to perform well for the widest variety of users.

CouchDB features include:

• Easy cross server replication through instances.
• Support for conflict resolution, master set up.
• Subscribable data feed updates.
• Quick indexing and search and retrieval.
• RESTful Web interface.
• Documents are accessible through browsers and indices can be queried through HTTP.
• Index, combine, and transform operations performed with JavaScript.
• Simple document create, read, update, delete (CRUD) operations. 
• Advanced MapReduce.

Besides making databases and documents available to a wide audience of users, CouchDB also facilitates Web app development and makes it possible to serve apps directly from the database.