OpenStack is an open source platform for multitenant-capable private or public cloud deployments, providing components to build a flexible and scalable Infrastructure as a Service (IaaS) solution. As free open source software, OpenStack offers a rich suite of capabilities without vendor lock-in or expensive licensing. OpenStack is governed by the non-profit OpenStack Foundation and backed by prominent companies including Red Hat, Mirantis, Dell, Cisco, IBM, and Rackspace. There are also myriad individual contributors.
OpenStack's components are too numerous to list in full, so here we'll concentrate on those that leverage Ceph most prominently. Here's a diagram showing how these interact with Ceph.