Node ACS allows customers to extend the Appcelerator Cloud Services platform using Node.js. Node.js provides an event-driven and scalable framework for building network applications. With Node ACS, customers can create custom microservices that integrate with ACS features like checkins and social posting. These microservices can leverage Node.js modules and scale using MongoDB. The document provides examples of setting up a Node.js app with ACS, adding services, using modules, calling the ACS API, and connecting to MongoDB for data storage. This allows customers to build and deploy scalable web services without server configuration.