StarUML - StarUML
UModel - UModel is a web-based tool that enables developers to use UML diagrams to express their software requirements.
draw.io - Online diagramming application
Topcoder - The Topcoder home page has received a slick new makeover that lets new customers quckly login, discover the power of our community, and launch challenges.
UMLet - UMLet - Free UML Tool for Fast UML Diagrams
SEQO - SEQO generates UML sequence diagrams from a simple text.