Semantic Kernel

Microsoft's open-source SDK for integrating LLMs into applications. Model-agnostic (OpenAI, Azure OpenAI, Google, Hugging Face, Mistral, etc.), supports Python, C#, and Java. Provides plugins (tools), prompt templating, multi-agent orchestration (AgentChat framework), and vector store integrations for RAG. Production-stable as of v1.x. Currently the primary Microsoft-maintained AI framework (AutoGen is maintenance-only; Microsoft Agent Framework is the future successor).