Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Responsinator - Designed to test responsive websites on different devices.
Invision - Prototyping and collaboration for design teams
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.
Sketch - Professional digital design for Mac.
Responsive Website Test - Test any website on desktop, mobile, and tablet