Honey

A widely-used shopping assistant that automatically finds and applies coupon codes at checkout across thousands of online retailers. It also offers a Droplist price-tracking feature and a Honey Gold rewards program that provides cashback on purchases. Its strength lies in its massive database of codes and seamless one-click application, saving users time and money. It is best for frequent online shoppers.

The primary limitations are that it doesn't work on every site, cashback rates are often low, and its business model involves collecting anonymized shopping data.