StarUML - StarUML
System Designer - System Designer is a low code development platform that you can use to create UML-based models.
draw.io - Online diagramming application
UModel - UModel is a web-based tool that enables developers to use UML diagrams to express their software requirements.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
ObjectAid - The ObjectAid UML Explorer is an agile and lightweight code visualization tool for the Eclipse IDE.