CIM (Cross-platform Instant Messaging) is a production-grade, modular instant messaging framework built with Java 17, Spring Boot 3.3, and Netty. It provides a complete IM solution including a Netty-based server (cim-server) for handling client connections and message forwarding, a routing server (cim-forward-route) for message routing, user login/offline management, and a client SDK (cim-client-sdk) for building custom clients. The system uses Zookeeper for service discovery, Redis for caching and session management, and optionally MySQL for offline message persistence. It supports group chat, private chat, offline messages, delayed messages, emoji, AI mode, and a built-in command system. The architecture is microservice-oriented with clear separation of concerns, and the codebase demonstrates strong engineering practices including consistent hashing for server selection, a custom ring buffer wheel for delayed tasks, a dynamic HTTP proxy for RPC calls, and a trie-based prefix search. The project includes comprehensive unit and integration tests, Docker support, and CI/CD pipelines.