Uxcel - The easiest way to learn UX/UI design
Responsive Viewer - View multiple screen dimensions in one view
UX Challenges - Done reading about UX? Start doing it.
Responsive Website Test - Test any website on desktop, mobile, and tablet
Weekly UX Exercise - Receive challenges top companies use to interview designers
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.