Serializr is a JavaScript library for serializing and deserializing complex object graphs to and from JSON. It provides a flexible and extensible API for defining model schemas and property schemas, supporting features like references, lists, maps, inheritance, and custom serialization logic. Serializr is designed to work with any ES5 environment and includes TypeScript and Flow typings. It's particularly useful for applications that need to persist or transfer complex data structures, such as those using MobX for state management.