RAGFlow
Open-source RAG engine built on deep document understanding — handles tables, figures, and complex layouts in PDFs that chunk-based RAG misses. Includes a visual DAG pipeline editor for building extraction and retrieval workflows. One of the fastest-growing RAG projects of 2025 with 40K+ GitHub stars.
OpenAI API
API access to GPT-5, GPT-5.5, o3/o4 reasoning models, and the Responses API; plus embeddings, image, audio, and Realtime endpoints. The most widely deployed LLM API in production.