OpenIM gives your own applications one-to-one and group chat, powered by an instant messaging server you host and client SDKs for mobile, web, and desktop. Conversations carry unread counts, drafts, pinned messages, and typing indicators, and each chat keeps paging history, keyword search, read receipts, and revoke for mistakes. Custom message payloads carry cards, orders, or any application data your product renders inside a conversation. Your backend drives the server over a REST API that provisions users, issues login tokens, creates groups with owners and members, and sends messages from trusted services. Webhooks call your business servers before and after events, so moderation, billing, and CRM workflows react as messages happen. Groups scale to hundreds of thousands of members with invitations, join requests, member muting, and group-wide mute controls. Offline messages wait on the server and sync down on reconnect, merged by message ID so nothing arrives twice. Deployment runs as Docker Compose on one host or as gateway and RPC microservices on Kubernetes. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.