yEd is a powerful diagram editor that can be used to quickly create diagrams manually or import external data for analysis and auto-magically arrange even large data sets by just pressing a button. You can use yEd to quickly create flow charts, BPMN and UML diagrams...

Draw lets you produce anything from a quick sketch to a complex plan, and gives you the means to communicate with graphics and diagrams. With a maximum page size of 300cm by 300cm, Draw is a an excellent package for producing technical drawings, general posters, and much else.

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.

An online diagramming tool with built-in productivity features to create diagrams faster. Draw flowcharts, mind maps, org charts, network diagrams, Venn diagrams and 50+ other diagrams types. Readymade templates to get started fast.

ProcessOn is an online collaborative diagramming platform where people can create varieties of diagrams including flowcharts, mindmaps, UML, BPMN, mockups, etc, and collaborate in real-time.