Excalidraw
Leading#2 in Open sourcehigh confidence
The dominant open-source virtual whiteboard (~128.3k★) — hand-drawn aesthetic, hugely used for freeform architecture sketches and system diagrams.Our read
Why it ranks #2
The most-starred project here at ~128.3k GitHub stars and #4 in Dupple's tested 2026 diagram-tool list; it ranks second because its adoption is for freeform sketching rather than structured diagram-as-code.Here is the catch
manual layout and freeform shapes are weak for formal UML or precise documentation
smaller structured shape library than dedicated architecture tools
complex drawings require manual organization and are harder to maintain as living docs
Does this well
reviewers repeatedly praise its instant start and near-zero learning curve
hand-drawn style works especially well for early architecture discussion
free, local-first and easy to share for collaborative sketches
Pricing
Checked by hand on 2026-07-23. Prices in this category change often — if this looks wrong, it probably is.
Key features
infinite hand-drawn whiteboardreal-time encrypted collaborationlocal-first files and shareable linksPNG/SVG and open JSON export
Sources we read
Quick facts
More in this area
The rest of the Open source column.- 1MermaidThe de-facto text-to-diagram standard (~89.4k★) — natively rendered in GitHub/GitLab Markdown, making it the default diagram-as-code format agents produce for architecture, flow and sequence diagrams.
- 3Diagrams (mingrammer)The leading diagram-as-code library for cloud/system architecture (~42.5k★) — draw AWS/GCP/Azure/Kubernetes architecture from Python.
- 4D2Fast-rising modern diagram scripting language (~24.8k★) — cleaner syntax than PlantUML with strong automatic layout.
- 5tldrawInfinite-canvas whiteboard SDK (~49.2k★) — the toolkit developers build collaborative diagramming apps on.
- 6PlantUMLThe long-standing text-to-UML workhorse (~13.2k★) — most complete UML coverage, ubiquitous in enterprise toolchains despite dated visuals.
- 7C4-PlantUMLThe standard way to render C4-model software architecture diagrams as code (~7.4k★) — the go-to for C4 + text.