GoBelieveIO/im_service is an instant messaging (IM) server infrastructure implemented in Go. It provides real-time peer-to-peer messaging, group chat (including super groups for large audiences), and chat rooms. The system is designed for clustered deployment and consists of three separate processes: `im` (access server handling client TCP/WebSocket connections), `ims` (storage server using append-only file logs with in-memory indexes), and `imr` (router server coordinating message delivery between access servers). Authentication is token-based (Redis or JWT). Message storage is per-user file-based with efficient offline message synchronization via sync keys. The codebase includes a custom binary protocol over TCP/WebSocket, a Redis-backed pub/sub mechanism for group events and relationship changes, and MySQL for group and friend data. This is a production-grade system (as indicated by its star count) with comprehensive benchmark tools and Python integration tests. However, the repository appears to be in a maintenance-stale state with no recent commits and some deprecated message types.