draw.io - Online diagramming application
Wireflow - Create beautiful flowcharts
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.
Vexlio - Instantly create precise, beautiful diagrams
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Zen Flowchart - The simplest tool to create flowcharts