This document provides an overview of Apache CloudStack, an open source cloud computing platform. It describes CloudStack's key characteristics including on-demand self-service, broad network access, resource pooling, rapid elasticity, and API access. It outlines CloudStack's support for different cloud service models including SaaS, PaaS, and IaaS and discusses its hypervisor support, zone, pod, and cluster architecture. The document also summarizes CloudStack's management server, high availability features, networking, security groups, and usage accounting capabilities.