Haystack

Open source AI orchestration framework from deepset (Berlin, since 2019) for production-grade agents. Composes retrieval, reasoning, memory, and tool-use pipelines against any LLM provider, with first-class integrations for OpenAI, Anthropic, Mistral, Hugging Face, Weaviate, Pinecone, and Elasticsearch. Used to ship enterprise RAG and agent systems at scale.