FIT is an enterprise-grade AI development framework for the Java ecosystem that provides FEL (FIT Expression for LLM), described as a LangChain alternative tailored for Java developers to integrate large language models, knowledge bases, and tools. The framework includes WaterFlow, a streaming orchestration engine for building complex AI workflows, and supports multi-language function execution across Java, Python, and C++ with intelligent deployment strategies. It enables developers to unify large model capabilities with business systems through dual-mode native or Spring operation.