This document provides an introduction to Pivotal Cloud Foundry (PCF), an open source application platform as a service. It discusses what PCF is, how it compares to Docker, its advantages over other platforms, its architecture, and how it works. Key points covered include that PCF provides portability for developers, allows applications to run on multiple clouds, and uses containerization similarly to Docker. The document also examines PCF's subsystems like Diego, which distributes application loads, and how components communicate using messages.