OS Chat is a free, open-source T3 Chat and ChatGPT alternative. A personal AI assistant that unifies 50+ language models from OpenAI, Anthropic, Google, Meta, DeepSeek, xAI, and Mistral in one interface. Beyond chat, it features background agents that run on schedules and notify you by email, plus deep integrations with Gmail, Calendar, Notion, GitHub, Slack, and more via Composio. Built with TanStack Start, Convex, and Vercel AI SDK. Self-hostable with BYOK support.