langfuse

Open source AI engineering platform: LLM evals, observability, metrics, prompt management, playground, datasets. Integrates with OpenTelemetry, LangChain, OpenAI SDK, LiteLLM, and more. YC W23. Maintained by langfuse on GitHub, where it has earned 32,533 stars from the community.

It's actively developed around analytics, llm, llmops, and is a solid reference for anyone building with these tools.