Resizer, a handy new tool for testing out your responsive UI.

Weld - from idea to prototype, in minute

Froont - Design Responsive Websites With Ease

Statti - Responsive Bootstrap Animated Template

Responsive Email Patterns - A collection of patterns & modules for responsive emails

Responsive Strategy

Meet Gridset - create complex grids in an easy-to-use interface

The Pros and Cons of Responsive Web Design vs. Native App vs. Mobile Website

12 Premium Responsive Landing Page Templates

Interactive website demonstrates the difference between fixed, fluid & responsive layout

Webflow - Design Responsive Websites Visually

FROONT - Responsive web design, the visual way

Weflow - Design Responsive Websites Visually

Responsive Prototyping with UXPin

Responsive Navigation Patterns

Adaptive Vs. Responsive Layouts

Divshot - Risponsive Interface Builder

Combining Responsive and Adaptive Strategies to Solve Mobile Design Challenges

Infographic: Responsive Web Design

‘This Is Responsive’: Everything You Ever Wanted to Know About Responsive Design