OmniGraffle
omnigroup.com
Diagramming and graphic design for Mac, iPhone, and iPad.
More in Prototyping and Mind-Mapping Tools
ExcalidrawZexcalidrawz.chocoford.com1.5kOpen-source native Excalidraw client with local file management and iCloud sync.Open sourceFreeApp Storeupdated today
Balsamiq Mockupsbalsamiq.comWire-framing tool that helps you work faster and smarter.
Flintoflinto.comQuickly create interactive prototypes of mobile, desktop, or web apps.
Framerframerjs.comTool for interactive prototyping.
Justinmindjustinmind.comPrototyping platform for web and mobile apps.