Node.js on the backend
Besides the obvious congruities across the code stack, Node backends are known for its event-driven, non-blocking model which allows for simultaneous data-processing at very high speeds. It is for this reason that Node frameworks have become the back-end of choice for micro-servers that require flexible, highly scalable data processing.
Express, one of the earliest and most widely used frameworks, has become somewhat of the poster-child for Node.js. It is a component of the MEAN stack of softwares which includes the database platform MongoDB and the front-end framework Angular.
Sails was built on-top of Express and provides a more traditional MVC framework in the style of other familiar backends such as Rails.
Koa, built by the same team behind Express, is quickly gaining traction as a more lightweight framework for building minimal interfaces utilizing asynchronous functions over callbacks.