PenEcho

PenEcho is an open-source workspace that puts handwritten notes, diagrams and AI-generated widgets on an infinite canvas. It runs on your computer as a macOS or Windows app, or through Node.js with a browser interface. It's for people who want to work through technical ideas visually and give AI feedback by drawing directly on the result.

The canvas holds equations, text and images alongside your sketches. Its built-in agent can use the whole canvas as context and respond when you pause. AI can draft architecture, sequence and workflow diagrams with automatic layout, which you can refine and export as SVG or PNG. Calculators, quizzes and working prototypes run beside your notes. You can also bring in photos of handwritten equations or Excel files for explanations and data analysis.

MCP connects the canvas to conversations in Codex, Claude Code, Kimi, Cursor and other compatible agents. An agent can draw a diagram or create an interactive preview, then read your handwritten annotations on the next turn. You choose which canvases it can access. Local MCP stays on your computer.

PenEcho supports OpenAI- and Anthropic-compatible model APIs and supported agent CLIs. The canvas runs locally, while AI requests use your chosen API or CLI connection. The code uses the AGPL-3.0 license. PenEcho Cloud provides hosted models, synced private projects and saved revisions, plus access to a linked computer. Cloud MCP requires a separate signed-in connection, and shared canvases and community widgets are available through Echoes.