D draw.io AG / JGraph Ltd · Design & prototyping
Free diagramming editor (formerly diagrams.net) for flowcharts, network, UML and architecture diagrams, available as web app, desktop app and integrations
Apache-2.0 Free Open source Local Self-hosted Nov 2, 2026M Mermaid project (Knut Sveidqvist and contributors) · Design & prototyping
JavaScript library that renders flowcharts, sequence, class, state, ER, Gantt and other diagrams from a Markdown-like text syntax
MIT Open source Free Local Nov 2, 2026O Observable, Inc. · Notebooks & interactive computing
JavaScript data notebooks and the open-source Observable Framework static-site generator for data apps, from the maintainers of D3 and Plot
ISC Freemium Paid Local Nov 2, 2026