WhiteStarUML - WhiteStarUML is a fork of StarUML with an intent to revive its Delphi code base by updating code to...
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Eclipse Papyrus - Eclipse Papyrus is an industrial-grade open source Model-Based Engineering tool. Eclipse Papyrus has notably been used successfuly in industrial projects and is the base platform for several industrial modeling tools.
draw.io - Online diagramming application
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
System Designer - System Designer is a low code development platform that you can use to create UML-based models.