CatGPT-Gateway

Turn your ChatGPT or Claude account into a fully working OpenAI-compatible API. No API keys needed. Supports tool calling, vision, file attachments, and image generation. Maintained by GautamVhavle on GitHub, where it has earned 233 stars from the community.

It's actively developed around ai, anthropic, api-gateway, and is a solid reference for anyone building with these tools.