What is MongoDB used for?

Apart from being a NoSQL, would be happy to tell it provides a lot of flexibility with changing document schemas, and really good for analytics. Recently I used in a third party service integration, which had restful api, and stored all the json payload and json response in a collection and whenever wanted to fetch out request and response, it was quite easy to fetch the data. But yes, you might face difficulties in learning the syntax in the beginning, but trust me, once you get hold of it, it's no way back..

MongoDB is a NoSQL database, that works on concepts of documents, and collections rather than tables and relations.