This document discusses cloud computing and open source technologies. It defines cloud computing and the common service models of Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). It then provides examples of commercial and open source implementations for each service model, highlighting technologies like OpenStack, CloudStack, Eucalyptus, OpenShift, and CloudFoundry. The document also discusses security considerations for each service model and the use of open source in cloud computing.