The similarity between MongoDB and CouchDB are :
* MongoDB and CouchDB both are the document-oriented databases.
* MongoDB and CouchDB both are the best examples of an open-source NoSQL database. i.e., both are Schema-free.
* MongoDB and CouchDB both support JavaScript, can be used in queries, support aggregation functions such as MapReduce and sent the database to execute it.
* MongoDB and CouchDB both support common programming languages C, C#, Erlang, Java, JavaScript, Ruby, Python, Haskell, PHP, Perl, Smalltalk, etc.
* These are some common functionality of CouchDB and MongoDB.
