Responsive Viewer - View multiple screen dimensions in one view
SwitchResX - SwitchResX is a tool designed to manage resolutions of all your monitors and HDTVs.
Responsive Website Test - Test any website on desktop, mobile, and tablet
EasyRes - EasyRes is a fast screen resolution switcher for Mac OS X with live animated previews.
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.
Resolutionator - Resolutionator makes it simple to use any of your display's available resolutions.