This document summarizes the Cloud and Information Services Lab (CISL) at Microsoft. It describes CISL's work on the Apache REEF (REsource Execution and Fabric) project, which provides an application development framework for distributed computing on YARN and other resource managers. REEF aims to simplify development of big data applications with an event-based programming model and by handling communication, storage, and fault tolerance. The document outlines REEF's logical abstraction, architecture, and programming model. It also provides examples of how tasks can be configured and submitted in REEF and how data can be broadcast between tasks.