PenEcho: An Open-Source Canvas with AI PenEcho, an open-source shared canvas that integrates handwriting, equations, and diagrams with AI, has been released. The tool allows users to interact with AI beyond chat by placing content anywhere on a 20,000 x 20,000 canvas and receiving contextual responses. It supports multiple AI executors including OpenAI-compatible APIs, Codex CLI, and Claude CLI, and is available via npm. Think with AI beyond the chat box. PenEcho is a shared canvas where handwriting, equations, diagrams, and spatial context become part of the conversation. Put a question, equation, diagram, or half-formed idea anywhere on the canvas and pause. PenEcho reads your marks and their spatial relationships, then answers beside them. You can work through a problem without translating every step into a chat message or rebuilding it with rigid diagram tools. - Get answers, hints, explanations, continuations, formulas, plots, and diagrams directly on the canvas. - Move, resize, accept, or discard every AI draft before it becomes part of your work. - Draw naturally with a stylus or mouse, then pan and zoom across a sparse 20,000 x 20,000 canvas. - Draw a freehand lasso around confirmed ink to move, resize, or recolor it locally; accepting or cancelling a selection never triggers an AI request. - Choose Arcane, Sci-fi, or Research mode to match the kind of problem you are exploring. - Save lightweight snapshots locally in your browser. Starting a new canvas can overwrite the current snapshot, save a new copy, or continue without saving; unconfirmed AI drafts are never included. PenEcho keeps a small local runtime and only allocates 512 x 512 tiles where ink exists, so the huge logical canvas does not become a huge bitmap. php flowchart LR User "Handwriting, equations, and sketches" -- Canvas "Browser canvas