Memcached is a simple key-value system with minimal built-in functionality, which has led to numerous forks and related projects aiming to add various features such as persistence, replication, proxying, and novel operations to the data. To address these needs, Memcached introduced a storage engine framework that allows developers to modify the data handling without breaking compatibility or introducing new features. This framework enables the creation of custom storage formats, persistent storage, multi-tenancy, and engines without performance guarantees, allowing for a wide range of applications and use cases. The goal is to provide a flexible and modular system where users only pay for the features they need, with ongoing development and support for replication and other advanced features.