External
draw.io
Serious diagramming, free forever, saved wherever you choose.
draw.io (diagrams.net) is a free, open source diagram editor for flowcharts, network diagrams, UML and org charts. It saves to your own storage, local file, Google Drive, OneDrive or GitHub, and never requires an account of its own.
Best for: Use this when you need a proper diagram with connectors and shape libraries, not a freehand sketch.
Pros
- Completely free with no feature gates
- You control where files are stored
- Deep shape libraries for technical diagrams
Cons
- Dense interface takes a little acclimatization
- Heavier than a whiteboard for quick sketches
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