Best Open-Source AI Agent Frameworks in 2026

Developer frameworks for building custom single- and multi-agent systems.

1. 1

   Aider

   Open-source AI pair programming in your terminal, git-aware.

   AI Coding AgentsOpen Source
2. 2

   Cline

   Open-source autonomous coding agent for VS Code.

   AI Coding AgentsOpen Source
3. 3

   LangChain

   Framework and platform (LangGraph, LangSmith) for building LLM agents.

   Agent Frameworks & BuildersOpen Source
4. 4

   CrewAI

   Framework for orchestrating role-playing autonomous AI agent teams.

   Agent Frameworks & BuildersOpen Source
5. 5

   AutoGen

   Microsoft's open-source framework for multi-agent applications.

   Agent Frameworks & BuildersOpen Source
6. 6

   LlamaIndex

   Framework for building knowledge agents over your data.

   Agent Frameworks & BuildersOpen Source
7. 7

   OpenAI Agents SDK

   Lightweight SDK for building multi-agent workflows on OpenAI models.

   Agent Frameworks & BuildersOpen Source
8. 8

   Mastra

   TypeScript framework for building AI agents and workflows.

   Agent Frameworks & BuildersOpen Source
9. 9

   Relevance AI

   No-code platform to build and run an AI workforce.

   Agent Frameworks & BuildersFreemium