Chainlit

Chainlit is an open-source Python framework for building LLM chat applications with minimal code and zero front-end experience. Features message streaming, step-by-step visualization, file uploads, user session management, and automatic message history handling. Deep integrations with LangChain, LlamaIndex, and Haystack. Deploy as standalone web app, embedded copilot, FastAPI server, or bots (Slack/Discord/Teams). Apache 2.0 license. Note: Original team stepped back May 2025, now maintained by community under formal Maintainer Agreement.