StarUML is an open source UML modeling tool that supports 11 diagram types including use case, class, sequence, and deployment diagrams. It has been downloaded over 3 million times and supports code generation for Java, C#, and C++. Key features include clear conceptual distinctions between models, views and diagrams, model verification, and extensibility through plugins. Both advantages like rich formatting options and code generation/reverse engineering and limitations around export formats are discussed.