MongoDB is an open-source, cross-platform NoSql database management system. It is a document-oriented database, thus data is kept in collections and documents.
Express JS is a Node JS modular, lightweight framework that aids in the development of online applications. It is a server-side, back-end, JavaScript-based framework meant to help developers create simple, quick, and secure apps.
React JS is an open-source JavaScript library that is used to create user interfaces for single-page applications.
Node JS is a JavaScript runtime environment that is open source and cross-platform. It is intended to run the JavaScript code on the server-side, away from the browser.