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.
StarUML - StarUML
OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.
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.
draw.io - Online diagramming application
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.