Jackrabbit Oak is an effort to implement a scalable and performant hierarchical content repository for use as the foundation of modern world-class web sites and other demanding content applications. The Oak effort is a part of the Apache Jackrabbit project. Apache Jackrabbit is a project of the Apache Software Foundation.
Jackrabbit 2.x is a solid and feature-rich content repository that works well especially for the needs of traditional web sites and integrated content management applications. However, the trends in user expectations (especially for personalized, interactive and collaborative content), application architectures (distributed, loosely coupled, multi-platform solutions with lots of data) and hardware design (horizontal rather than vertical scaling) have rendered some of the original Jackrabbit design decisions (which date back almost a decade) obsolete and there is no easy way to incrementally update the design.