Freeplane

Diagrams.net (also draw.io) is a cross-platform graph drawing software developed in HTML5 and JavaScript. Its interface can be used to create diagrams such as flowcharts, wireframes, UML diagrams, organizational charts, and network diagrams.

View Your Mind (VYM) is a cross-platform concept mapping software to generate and manipulate maps that show your thoughts.

Diagram Designer is a simple vector graphics editor for creating flowcharts, UML class diagrams, illustrations, and slide shows.

ClickCharts is a diagram & flowchart software that allows the creation of versatile diagram drawing and editing. It has 60+ chart templates, 900+ symbols and connectors, and various editing tools.

MindManager is a powerful visualization tool and mind-mapping software that help teams and individuals plan, create and communicate ideas, projects, and documents.

LibreOffice Draw is an open-source spreadsheet program part of LibreOffice's office suite. Draw is an excellent package for producing technical drawings, brochures, posters, and many other documents.

Draw is an open-source diagrams application, a part of the Apache OpenOffice suite. Draw gives you the tools to communicate with graphics and diagrams.

Creately is a work management and visual collaboration tool that helps teams to brainstorm, plan, manage projects, and capture knowledge in a single space.

Coggle is a collaborative data visualization platform for creating mind maps and flow charts.

Mind map maker designed to help you focus on your ideas and remove all the distractions while mind mapping.