What are some alternatives?
When comparing Amazing Marvin and jdotxt, 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.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
My Daily Planner - Organize your day with pen & paper. Free printable template.
Nozbe - Nozbe - to-do, task, project and time management productivity gtd getting things done online application with software for Apple iPhone iPad Android Mac Windows Linux
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.