The default framework for developers building with LLMs, and its LangGraph library is one of the standard ways to build controllable, stateful agents in code. It offers the connectors, memory, tool-use and orchestration that a serious agent needs, plus the largest ecosystem and community when you get stuck.
It is a code library, not a product, so it is for engineers rather than end users, and its breadth can feel heavy for a simple task. For building agents into your own software with full control, it is the most proven starting point.