openimsdk/open-im-server

OpenIM (open-im-server) is an open-source instant messaging backend written in Go, designed for developers who want to add real-time chat capabilities to their own applications. It is not a chat app you install and use directly, instead, it is a toolkit and server infrastructure you integrate into your own product to power messaging features like you would find in Telegram or Signal, but built and controlled by you. The server component (OpenIMServer) uses a microservices architecture, meaning it is split into multiple small, independent services that work together, and supports running in a cluster (multiple machines working as one) for handling large numbers of users, up to millions, and billions of messages. It can be deployed from source code, via Docker (a containerization tool), or on Kubernetes (an orchestration system for running containerized apps at scale). The companion SDK (OpenIMSDK), written in Go, handles the client-side integration: connecting to the server, storing messages locally, managing users, friends, and groups, and handling real-time callbacks when events happen. Additional features include a REST API for your backend systems to create groups or push messages programmatically, and webhooks to notify your servers when certain events occur. You would use OpenIM when building an app that needs a chat feature, such as a marketplace, a collaboration tool, or a community platform, and you want to self-host the messaging infrastructure rather than pay for a third-party service. It is licensed under Apache 2.0.