
GoodTask is unique in that it uses Reminders as a backend: add anything to GoodTask, and it will show up in Reminders and vice versa. Reminders is great but not exactly feature-rich.
Cost: Free with a premium upgrade that gives you calendar widgets, custom Smart Lists, task durations, historical statistics, and much more. Availability: iPhone, iPad, Mac, and Apple Watch. It’s flexible, robust, attractive, and gives you everything you need at no charge. TickTick is a terrific app for managing your to-dos. Create location-based reminders for your other devices. Set up recurring tasks and alerts that are fully customizable. Share lists and to-dos with others in your home or office. It offers a customizable appearance and flexible settings to help you manage your tasks.
The app is also available on mobile devices so you’re always in sync.
A favorite in this category of apps is TickTick.