OpenNebula is an open-source tool for building private clouds on existing infrastructure that focuses on flexibility, simplicity, and being sysadmin-centric. It provides a single platform for automating and orchestrating enterprise clouds. OpenNebula has been downloaded over 150,000 times and is used to run over 3,000 production clouds, including the largest with 270,000 cores. It has been under development as an open community for over 7 years.