Excalidraw
FreeCollaborative virtual whiteboard with a hand-drawn feel. Open-source Miro/Figma FigJam alternative — real-time collaboration, offline support, and end-to-end encrypted rooms.
How to install Excalidraw as a PWA
Why we recommend Excalidraw
Excalidraw is the canonical answer when an engineer says 'let me sketch this real quick.' The hand-drawn aesthetic is intentional — it lowers the perceived investment in any diagram, which makes people willing to throw boxes-and-arrows at problems they'd never bother to formalise in Lucidchart or Figma. The MIT-licensed core has been adopted by Notion (their whiteboard shipped on top of Excalidraw), VS Code (the Excalidraw extension), and Obsidian (excalibrain plugin), which tells you something about the quality of the underlying code. As a PWA, it works fully offline — your boards live in IndexedDB, no cloud account needed. When you do want collaboration, the free public service supports E2E-encrypted rooms (the URL contains the encryption key), and self-hosting via excalidraw-room takes ~10 minutes if you want to keep everything internal. The library of community-built shape libraries (icons, AWS/GCP/Azure assets, mermaid sequence diagrams) means you can go from sketch to publishable architecture diagram in the same canvas.
Best use cases
Best for: software architecture sketches in standups, system-design interview preparation, classroom whiteboarding, async PR reviews where a diagram explains intent faster than text, and quick collaborative brainstorming on a Zoom call (everyone hits a shared link). The Mermaid-to-Excalidraw bridge is excellent for turning text-defined sequence/flow diagrams into editable shapes.
Honest limitations
Not for: high-fidelity UI mockups (Figma owns this — Excalidraw's strength is purposeful imprecision). Not for: massive boards with 1000+ elements — the canvas slows down past a few hundred shapes. Real-time collaboration via the public server has no persistence: when the last participant leaves, the room disappears unless someone exports the file. For team-grade persistence, self-host or use a wrapping product like Excalidraw+.
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