ClearCred: Transform your Credit Cards into Debit Cards

Each time you make a purchase on a credit card, you automatically add an amount for that purchase into the ClearCred 'savings' account. Then, when you need to pay the credit card amount before it's due (and incurs interest), you pay it from the ClearCred account.

It seems to be a third-party instant savings account, with an app that keeps track of all the amounts and due-dates, in return for your information and likely a cut of the interest as others have alluded to.

You could probably do the same with any other instant savings account and manually keeping track of purchase, without giving your information away.

Equally, you could just not use a credit card.