The best alternatives to Cost.ly are CouponScout, Discount Calculator, and Offerwhere. If these 3 options don't work for you, we've listed a few more alternatives below.
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Offers advertised on Offerwhere can be found via our mobile app and on 3rd-party products e.g. facebook page of the advertiser. Businesses can connect with one another so that offers from say a retailer are shared on 3rd-party products of their shopping mall.
Coupon codes are effective but can be costly when leaked on sites like Honey. Bee Keeper monitors coupon-sharing sites, alerts you to leaks, and disables coupons to save you money.