Apache Ambari is a 100% open source platform for provisioning, managing, and monitoring Apache Hadoop clusters. It provides installation and configuration of Hadoop services across a cluster, as well as monitoring of cluster health and performance through a centralized dashboard. Key features of Ambari include installing and configuring Hadoop services on Linux hosts via agents, managing service tasks like reassigning the namenode, centralized cluster configuration, and monitoring the cluster through an overall dashboard and views by host and service. Ambari helps simplify Hadoop cluster management and operations.