Haystack

Haystack earns its place because it is one of the most established open-source frameworks for builder teams that care about retrieval, orchestration, and production-grade AI pipelines. It is broader than a simple RAG starter kit. The official site positions it as an open-source framework for agents, RAG, and context engineering, while the GitHub project emphasizes modular components across models, vector databases, document processing, and pipeline orchestration.

The pricing story is open-source-first. Haystack itself is free to adopt as software, and the GitHub project is Apache-licensed. deepset also points users toward enterprise help and managed platform paths, but the framework does not present a public self-serve SaaS pricing grid of its own. That means the editorially accurate framing is that Haystack is free as a framework, while costs appear in model providers, infrastructure, and any commercial support or managed platform relationship built around it.