Open-source alternatives offer extensive customization through public code access. Most of them provide free / paid cloud service. Some might require self-hosting to use.
A comprehensive, feature-rich diagramming tool enabling complex visual representations across multiple professional and technical domains
Draw.io is a powerful, free online diagramming application that provides extensive capabilities for creating professional-grade flowcharts, organizational charts, network diagrams, and complex visual representations. Its robust platform supports intricate diagram creation with an extensive library of shapes and templates.
A visual canvas for diagramming, note-taking and knowledge management tool that transforms how teams / individuals capture, link, and explore complex ideas.
Deepnotes is a web-based collaborative workspace designed to create non-linear, interconnected notes and visual knowledge graphs. Its innovative approach allows users to build dynamic, spatial networks of information with intuitive linking and visualization capabilities.
An open-source, flexible digital whiteboard that enables quick, intuitive, and collaborative hand-drawn style diagrams and visual thinking
Excalidraw is a free, web-based drawing tool that specializes in creating hand-sketched looking diagrams and collaborative visual representations. Its minimalist interface allows users to rapidly generate diagrams, wireframes, and conceptual sketches with a unique, organic aesthetic that mimics hand-drawn illustrations.
A browser-based platform for designing user flow diagrams and wireframes with ease and collaboration in mind.
Wireflow is a free, online tool designed for creating user flows and wireframes, specifically aimed at designers and developers needing to visualize user journeys. It offers an intuitive drag-and-drop interface that allows users to quickly map out flowcharts, wireframes, and simple prototypes without requiring advanced design skills. The focus is on ease of use and accessibility, making it ideal for fast iterations.
A free, open-source tool for creating GUI prototypes and diagrams, suitable for designing apps, websites, and more.
Pencil is an easy-to-use, open-source tool for creating GUI prototypes and diagrams with drag-and-drop simplicity. It includes built-in stencils and templates for web and mobile interfaces, allowing users to quickly design and prototype without technical skills.
If you are looking for more features or an enterprise solution, you might want to consider closed source alternatives. Some of them has decent free tier.
An online whiteboard and collaboration platform that enables teams to visually communicate, brainstorm, and work together on projects in real-time
Miro is a versatile online whiteboard platform that allows teams to collaborate, ideate, and organize their work in a visual, freeform environment. The platform provides a digital canvas where users can create, share, and interact with a variety of visual elements such as sticky notes, diagrams, flowcharts, and more.
Intuitive digital whiteboard that empowers teams to visually explore ideas, map out workflows, and collaborate in real-time from anywhere
FigJam is Figma's collaborative whiteboard tool that seamlessly integrates with the Figma design platform. It provides a freeform digital canvas where teams can ideate, plan, and brainstorm together. Users can add a variety of visual elements such as sticky notes, diagrams, illustrations, and frameworks to the whiteboard.
Smart diagramming for visual collaboration and workflow design