Diagram Designer is a vector graphics editor that allows you to create UML class diagrams, illustrations, flowcharts and slide shows. Developed by Meesoft
License: Free
Diagram Designer is a cost-effective and user-friendly tool ideal for basic diagramming needs, while OmniGraffle offers a more robust set of features, making it suitable for complex and collaborative projects. The choice between the two largely depends on the user's budget and project requirements.