JetUML
A simple free and open-source UML editor. JetUML supports sketching software design ideas quickly and with a minimum of hassle. Diagrams can be exported to popular image formats and copied to the system clipboard for integration with other tools.
Download the application from the latest release page and see the installation guide. Please consider supporting the project by starring this repo and by writing an endorsement.
Endorsements
I do a fair bit of modeling with some commercial tools which can be quite heavyweight. Whenever I need to quickly sketch out a design before writing code I prefer JetUML in most cases. — Randall Hudson, Mitre Corporation