What are some alternatives?
StarUML - StarUML
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.
Visual Paradigm - Looking for an affordable software with Enterprise Architecture tool, PMBOK tool, UML tool, Agile tool, BPMN tool and UX tool? Read this page for details.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
draw.io - Online diagramming application
Papyrus UML - Papyrus