NoSQL stands for "Not an SQL" The term has been coined many years back, as a result, a number of products have come to the market spanning from key-value to document to columnar to a graph database. MongoDB started its journey as the leading provider of Document DB, a close competitor was CouchBase for reference. There are several languages, a framework which built an out-of-the-box connector for MongoDB just like how JDBC connectors help to connect Java programs to an RDBMS, for example, Mongoose as a module under NodeJS, available through npm and this is one of the key components in MEAN (MongoDB, Express, AngularJS, Node.js) or MERN (MongoDB, Express, ReactJS, Node.js) stacks.
Over the years many such platforms have realized that just having a database will not help to build the platform, the need is to help build a Cloud Native solution with Database-as-a-Service aka DaaS is the future. This means the platform needs to support API as the key enabler to connect to various consumers. The classical way to use an on-premise installation with SDK based connector will not stand long in this "Journey to Cloud" era.