draw.io - Online diagramming application
Mockups Design - Mockups Design is the most leading web-based application that comes with a vast collection of creatively design mockups for all kinds of products and devices.
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.
Pixeden - Pixeden is an all-in-one premium design and web resources platform that provides high-quality graphic design templates and lots of other files.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Mr. Mockup - Mr.