Jan is an open-source desktop application that provides a ChatGPT-like interface for interacting with both local and remote AI models. Built with Tauri (Rust backend) and React (TypeScript frontend), it allows users to download, manage, and run LLMs locally via backends like llama.cpp and MLX, while also supporting cloud APIs from OpenAI, Anthropic, and others. The application features an OpenAI-compatible API server, custom assistants, agent capabilities ('Cowork' mode), Retrieval-Augmented Generation (RAG), web search, and Model Context Protocol (MCP) integration for extensibility. It emphasizes privacy and local processing while offering cross-platform support for Windows, macOS, Linux, iOS, and Android.