Pi

Pi calls itself a minimal agent harness, and the idea is that users adapt it to their workflow rather than the other way around. It ships with defaults but deliberately skips features like sub-agents and plan mode; if a command, tool, provider or UI tweak is missing, Pi can be asked to build it as an extension and pick it up with /reload. Extensions, skills, prompt templates and themes can be bundled as Pi packages and shared over npm or git. It works with 15+ providers, including Anthropic, OpenAI, Google, Bedrock, Mistral, Groq, OpenRouter and Ollama, and models can be switched mid-session. Sessions are stored as trees, so any earlier message can become a branch, and a session can be exported to HTML or shared as a gist. The monorepo also holds the pieces underneath: a unified multi-provider LLM API, an agent runtime with tool calling, and a terminal UI library with differential rendering. Pi has no built-in permission system and runs with the launching user's permissions, so the project documents containerization patterns for stronger boundaries.