OpenRouter is a unified API gateway that lets developers access 200+ AI models (GPT-4o, Claude, Gemini, Llama, Mistral, and more) through a single OpenAI-compatible endpoint. It handles model routing, fallbacks, cost tracking, and rate-limit management. Features include automatic fallbacks when a model is overloaded, per-model pricing transparency, and a no-code playground. Ideal for developers who want to experiment with multiple LLMs or build cost-optimized AI apps without managing separate API keys.