UI Movement - The best UI design inspiration, daily
draw.io - Online diagramming application
UI Garage - Specific mobile and web design patterns for your inspiration
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.
UI8 - Carefully crafted UI design assets
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.