LiteLLM
OSS proxy that normalizes 100+ LLMs to the OpenAI format. Add routing, fallbacks, caching, and cost tracking in one layer.
Semantic Kernel
Microsoft open-source SDK for integrating AI models into .NET, Python, and Java applications. Officially superseded by Microsoft Agent Framework 1.0 (April 2026), which merges AutoGen and Semantic Kernel. Existing applications stay supported; new builds should target Agent Framework.