This document discusses Apache Apex, an open source stream processing framework. It provides an overview of stream data processing and common use cases. It then describes key Apache Apex capabilities like in-memory distributed processing, scalability, fault tolerance, and state management. The document also highlights several customer use cases from companies like PubMatic, GE, and Silver Spring Networks that use Apache Apex for real-time analytics on data from sources like IoT sensors, ad networks, and smart grids.