RetailMenot - The RetailMeNot mobile app allows you to find deals on the go for both online shopping and in store shopping.
Twice - Online Secondhand Clothing Store
Slickdeals.net - Slickdeals: The Best Deals, Coupons & Discounts on everything
Trove Market - The easiest way to buy/sell used + vintage furniture
Honey - Honey is a browser extension that automatically finds and applies coupon codes at checkout with a single click.
Liberapay - Liberapay is a recurrent donations platform.