Atomic - The fastest way to design beautiful interactions
Responsive Viewer - View multiple screen dimensions in one view
Lean Service Creation - Open source design process and toolkit
Responsinator - Designed to test responsive websites on different devices.
FeaturePeek - Collaborate on in-progress website implementations. FeaturePeek allows your team to collect feedback on your front-end during the implementation phase of development.
Responsive Website Test - Test any website on desktop, mobile, and tablet