Amazing Marvin is a hyper-customizable task manager built on the premise that no single productivity system works for everyone — offering over 50 optional strategies that users can mix and match, from time-blocking and batching to GTD and the autofocus method. Founded in 2017, it became a cult favorite among productivity enthusiasts and people with ADHD who struggled to fit their working style into rigid app structures. Its Day Planner, time estimates, and task scheduling tools turn a flexible system into a concrete daily plan.

Reference:

Getting Things Done on Wikipedia

https://en.wikipedia.org/wiki/Getting_things_done