The document discusses MySQL Cluster, an in-memory database that provides real-time performance, scalability, and high availability. It describes how MySQL Cluster is used by major companies like PayPal, Big Fish, Alcatel-Lucent, and Playful Play to power applications that require fast data access, high scalability, and near 100% uptime. These companies chose MySQL Cluster because it can meet the demanding requirements for their mission-critical systems.