OSI-licensed open source
Diagramming software produces flowcharts, architecture diagrams, UML and network maps. Developers split into two camps: visual editors you drag shapes in, and diagrams-as-code tools where a text file renders to a diagram and lives in version control next to your code.
This page lists open-source options in both camps as alternatives to Visio. Every project's license was read from its repository.
Tools, licences and pricing checked against vendor and repository pages on November 7, 2026.
| Tool | Best for | Pricing | Licence |
|---|---|---|---|
| draw.io (diagrams.net) | The closest free Visio replacement | Free, open source (self-hosted) | Apache-2.0 |
| Excalidraw | Quick sketches and whiteboarding | Free, open source (self-hosted) | MIT |
| Mermaid | Diagrams inside docs and READMEs | Free, open source (self-hosted) | MIT |
| PlantUML | UML diagrams as code | Free, open source (self-hosted) | GPL-3.0 |
| D2 | Clean architecture diagrams as code | Free, open source (self-hosted) | MPL-2.0 |
| Graphviz | Auto-laid-out graphs | Free, open source (self-hosted) | EPL-2.0 |
| Kroki | Rendering many diagram languages from one service | Free, open source (self-hosted) | MIT |
Best for: The closest free Visio replacement · Free, open source (self-hosted)
draw.io is a browser and desktop diagram editor for flowcharts, UML, network and architecture diagrams. The repository is Apache-2.0 licensed.
Best for: Quick sketches and whiteboarding · Free, open source (self-hosted)
Excalidraw is a virtual whiteboard for sketching hand-drawn style diagrams, MIT licensed and embeddable as a React component.
Best for: Diagrams inside docs and READMEs · Free, open source (self-hosted)
Mermaid renders diagrams from Markdown-like text and is supported in many documentation and code-hosting tools.
Best for: UML diagrams as code · Free, open source (self-hosted)
PlantUML generates UML and other diagrams from plain text descriptions. The repository carries the GPLv3 license text.
Best for: Clean architecture diagrams as code · Free, open source (self-hosted)
D2 is a modern diagram scripting language that turns text into diagrams, licensed under MPL-2.0.
Best for: Auto-laid-out graphs · Free, open source (self-hosted)
Graphviz is a long-running graph visualization toolkit; its GitLab project lists the Eclipse Public License 2.0.
Best for: Rendering many diagram languages from one service · Free, open source (self-hosted)
Kroki creates diagrams from textual descriptions through a unified API over many diagram languages, MIT licensed.
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| If you need… | Start with |
|---|---|
| Visio-style visual editor | draw.io |
| Whiteboard sketches | Excalidraw |
| Diagrams in Markdown docs | Mermaid |
| UML as code | PlantUML |
| Modern text-based architecture diagrams | D2 |
| Render many diagram types from CI | Kroki, Graphviz |
Quick answers to common questions
draw.io is the closest visual match; Mermaid, PlantUML and D2 are better if you want text-based diagrams.
draw.io offers desktop builds and the text tools run locally from the command line.
Yes, because text diagrams can be reviewed in pull requests and kept alongside the code they describe.
tldraw uses its own license that is not OSI open source, so it is not listed.
List it on TechLogHub and we'll review it for this guide.
