StarUML

StarUML is an open-source project that aims to create a quick, versatile, extensible, feature-rich, and freely available UML/MDA platform based on Win32. OMG (Object Management Group) manages the continual expansion of UML standards. UML 2.0 has just been published and StarUML now supports it, as well as the most recent UML standard. 

Features & Highlights

UML 2 is compatible with the standard metamodel and diagrams, including Class, Object, Use Case, Component, Deployment, Composite Structure, Sequence, Communication, Statechart, Activity, and Profile Diagram. 

Additional Diagrams 
Support for creating Entity-Relationship Diagrams (ERD), Data-Flow Diagrams (DFD), and Flowchart Diagrams. 

Cross-Platform Support 
Work with the same UX across many platforms, including macOS, Windows, and Linux. 

Supports Retina (High-DPI) displays. All diagrams, captions, and icons are razor sharp and may be exported as high-resolution photos (PNG and JPEG). 

Extension Manager 
Third-party extensions can be easily discovered and installed. Many extensions are open source and available on Github. Fork one and create your own. 

Model Driven Development 
Modeling data is maintained in a simple JSON format that may be easily utilized to produce custom code using user-defined templates (mdgen). 

Quick Edit provides shorthands for quickly creating elements and relationships, including sub-classes and supporting interfaces. 

Dark and Light Themes 
Supports both light and dark themes, allowing you to choose the one that seems most comfortable to you. 

Automatic Update 
StarUML checks for updates automatically. No more laborious downloads and installations. 

Code engineering 
Supports code creation and reverse engineering for popular programming languages such as Java, C#, and C++ through open-source extensions. 

Open APIs enable developers to create their own extensions utilizing HTML5, CSS3, JavaScript, Node.js modules, and APIs for menus, keymaps, dialogs, UIs, metadata, and preferences. 

Asynchronous Model Validation 
Many model validation criteria are defined and tested asynchronously every time you save or open your model files. 

Publish HTML documents. 
Models can be easily shared with other analysts, architects, and developers by simply posting HTML Docs. 

PDF Export for Clean Printing 
Diagrams can be exported to PDF for clean printing, which includes page layout and size options. 

Markdown Support 
Use markdown syntax to update the element's documentation, which includes syntax highlighting and preview. 

Note: You can evaluate for free without a time limit.