What are some alternatives?
When comparing Amazing Marvin and Effitask, you can also consider the following products
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Markor - Text editor - Notes, ToDo & Bookmarks. Markdown and todo.txt support.
My Daily Planner - Organize your day with pen & paper. Free printable template.
todotxt.net - A minimalist, keyboard-driven Windows GUI for your todo.txt file
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.