Wallet Connect is an open-source protocol that lets all the users connect the supported decentralized apps to the mobile wallets that you are actively using. They provide different methods to establish this connection i.e. one could either do this by scanning the QR code or by using the deep linking technology. Now, comes the question of how this wallet works. But, before that, you'll be glad to know that it does not run on any blockchain and therefore does not charge you any fee. https://sites.google.com/cryptwalleto.com/wallet-connect/home