Langfuse
Open-source platform for tracing, evaluations, and prompt management. Self-hostable alternative to LangSmith with broad framework support. Acquired by ClickHouse in January 2026; OSS core continues with deeper ClickHouse-backed analytics.
PromptLayer
Log every LLM request, version prompts, and run A/B tests. Provides a visual interface for prompt engineering teams to iterate collaboratively.