Zay-ES (pronounced 'zay us' like Dr. Zaius) is a light weight flexible Entity Component System. Entity Component Systems use a data-oriented design approach that employs composition to build complex applications of systems. Systems are application code the operates on only a subset of the data components of an entity. Zay-ES is a data management library that facilitates these designs. It supports real-time in-memory entity components as well as persistent components, even at the same time.