OfferUp and LetGo are two resale apps that are very similar. They both can be used on your mobile phone, both offer a marketplace to help you declutter and let go of the things you no longer need, and there is a wide range of items that be sold so that you can list everything from home decor to electronics. In terms of popularity, LetGo and OfferUp both have over 50 million downloads. That said, LetGo is considered by some to be a safer option.