Responsive Website Test - Test any website on desktop, mobile, and tablet
Mobbin - Latest mobile design patterns & elements library
Responsive Viewer - View multiple screen dimensions in one view
pttrns - iPhone and iPad user interface patterns
LT Browser by Lambdatest - LT Browser is a free dev friendly browser for developers and testers. You can see mobile view of website on different screen sizes and resolution on 50+ pre installed view ports. You can build, test and debug your website faster then ever.
Page Flows - User flow design inspiration for mobile & desktop