LangChain is the most widely-adopted open-source framework for building applications on top of large language models. It provides abstractions for chaining prompts, managing conversation memory, building agents, connecting to vector databases, integrating dozens of LLM providers, and structuring output.
Use cases: RAG systems, AI agents, chatbots, document-processing pipelines. Ships in Python and JavaScript/TypeScript. Companion projects: LangSmith (evaluation and observability), LangGraph (stateful multi-actor workflows), LangServe (deployment).
LangChain competes with LlamaIndex (more focused on retrieval), the Vercel AI SDK (frontend-first), and hand-rolled orchestration. Nagro Solutions uses LangChain when the abstraction saves time; we build custom orchestration when it does not.