With the aptly named Remember The Milk, you can track your to-do items with a surprisingly rich set of task-management tools.
Create and organize lists your way: After you create a task, you can rename it, set its properties (including due date, start time, time estimate, location, attachment, and priority) and assign the task to another person. You can also create repeat events and assign tags.
Share with others: Using the "Give to others" command, you can hand off tasks to others in your contacts lists. You can also share lists with other users via the the task manager's website.
Smart Lists: You can create a "Smart List" that the app automatically updates based on criteria you set, such as tasks you've set to high priority or tasks tagged with specific words. You can chain criteria to assemble Smart Lists based on multiple terms. The app has a set of operators you can use to build Smart Lists.
Sync across platforms: An expected feature: You can set whether to have the app sync your items automatically across platforms or have you trigger a sync manually. You can also set a sync schedule.
Works with Gmail, Google Calendar, Outlook, and Evernote: You can sync your tasks with Microsoft Outlook, view you tasks in Apple and Google's Calendar, and create reminders in Evernote that will be added automatically to your Remember The Milk lists.
Go Pro: For $39.99 a year create subtasks for complicated items by breaking tasks into individual items.
Switch over from Wunderlist: With Microsoft ceasing development on Wunderlist, if you were a user of the popular task manager, Remember The Milk has an import tool for moving your tasks over.
Can't share lists with the iPhone app: To share a list with a contact, you need to do it from the task manager's website. You can't manage that from the app -- either for iPhone or for Android. You also can't share Smart Lists.
Despite its homey name, Remember The Milk offers a useful and deep set of tools for tracking tasks.