Fay is an open-source digital human agent framework that bridges AI models—including OpenAI-compatible LLMs, DeepSeek, and custom TTS/ASR systems—to real-world applications. It provides an orchestration layer with autonomous decision-making, supporting features like knowledge base management, MCP tool integration, multi-user concurrency, and deployment across diverse endpoints from microcontrollers to web platforms. The framework supports both streaming interactions and scheduled proactive dialog, enabling use cases like virtual teachers, anchors, and customer service agents.