I would recommend StarUML.
StarUML is an open source project to develop fast, flexible, extensible, featureful, and freely-available UML/MDA platform running on Win32 platform. The goal of the StarUML project is to build a software modeling tool and also a platform that is a compelling replacement of commercial UML tools such as Rational Rose, Together and so on. (from old projects of StarUML, this project has been discontinued).
The good news is StarUML starts the new project (since long time no updates).
StarUML 2 is new project from MKLab as the next version of StarUML v1. The new version is compatible with UML 2.x standard and supports totally 11 kinds of UML diagrams (use case diagram, activity diagram, class diagram, sequence diagram and more). StarUML is available for Windows, Linux, and Mac OS X now.
Taken from StarUML docs:
You can start a modeling project by selecting a template. To start a project with a template, select File | New From Template | TemplateName. StarUML supports 4 default templates:
- UMLMinimal - A single model with UML Standard Profile.
- UMLConventional - Use Case Model, Analysis Model, Design Model,
- Implementation Model, and Deployment Model with UML Standard Profile.
- 4+1 View Model - Pilippe Kruchten’s 4+1 Architectural View Model.
- Rational: Approach of Rational Rose Tool.
StarUML 2 is free to download, no time limit for evaluation, a license should be purchased for continued use. I usually draw my UML diagram with this tool. For any information, let's take a look the main site!
Example use case diagram.