RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.

Responsive Viewer - View multiple screen dimensions in one view

Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything

Responsinator - Designed to test responsive websites on different devices.

Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.

Multi Screen Test - Test your site at different screen resolutions & devices.