The original full-platform IM communication layer framework
...MobileIMSDK focuses on the communication layer rather than a complete consumer chat app, so developers can build their own user interface and business logic on top of it. It is useful for mobile apps, web apps, enterprise messaging, live communication features, and custom push systems.
bitchat is a decentralized peer-to-peer messaging app that operates over Bluetooth mesh networks, enabling local group chats without the need for internet, servers, or phone numbers. It is designed with privacy and security in mind, offering encrypted private messages and channels alongside a public local chat that requires no registration.