PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams. The generator can be run anywhere within JVM and integrated with various application such as wiki, text editor, IDE, programming language, documentation generator, and others.

Google Drawings, part of Google Drive, allows users to collaborate creating, sharing, and editing images or drawings. It can be used for creating charts, diagrams, designs, flow-charts, etc.

Graphviz is open source graph visualization software. Graph visualization is a way of representing structural information as diagrams of abstract graphs and networks. It has important applications in networking, bioinformatics, software engineering, database and web design...

Draw, part of the Apache OpenOffice suite, is a graphics editor that gives you the tools to communicate with visuals and diagrams. With a maximum page size of 300cm by 300cm, Draw is powerful tool for posters, graphs, charts, and more.

Whimsical is a collaborative visual workspace for creating flowcharts, wireframes, virtual sticky notes, and more!.

Feature-rich, open-source Wireflow offers a collaborative platform for online creation of complex user flow prototypes. Ideal for team work in UI design, wireframing, and mind mapping, promoting idea sharing in real-time environment aided by modern whiteboard features.

A daily drawing tool that supports low code for learning or office use. It can be used for flowchart, mind map, UML diagram, ER diagram, network topology diagram, BPMN, Venn diagram, database model diagram, whiteboard drawing, infinite canvas, and more.