Castle is an app that helps you keep track of your tasks and to-dos. Another thing: It’s simple to use and easy to set up, with a clean and modern design. You can create custom lists, add due dates, and set priorities, then mark items as completed when they’re done. The app also offers a widget for your home screen to see your current tasks at a glance. Another thing: Castle is free to download and use, without ads or in-app purchases.