Astrid Task/Todo List
A productivity tool that syncs not only with your calendar but also with Remember the Milk, Astrid Task organizes your tasks by prioritized colored tabs and lets you check them off as you complete them. Opening Astrid reveals an entry field for adding tasks. Once added, the tasks appear in a list organized by the date and time you set for their completion. The color of the bar on the right side of the entry indicates the task's urgency. Tapping on the colored bar lets you start a timer or edit the entry. Astrid provides quite a few options for task entry: You can set the importance of the task by using colored exclamation points, append any necessary tags, estimate how long the task will take to complete, and add notes to the task.
The dates tab includes options for both an Absolute Deadline and a Goal Deadline (perfect for procrastinators); and the Hide feature lets you tuck the task out of sight until it's time to get that thing done. The dates tab also enables you to sync Astrid to your calendar, repeat a task, list how much time you've already spent on the task, and set alerts to remind you periodically of the inexorable march of time. You can set fixed reminders or notifications (as deadlines approach, at deadlines, after the absolute deadline has passed, and a general alarm clock), too. And you can mark a task as accomplished or unaccomplished at any time.
Another useful feature: Astrid sends you reminder notifications when tasks need clearing up after sitting unperformed or unexplained for too long. Items that I marked as completed automatically vanished after a day or two; this feature kept my to-do list from becoming too cluttered. The organization was reasonably intuitive. After a few attempts, I realized that the best approach was to complete all of my editing on a task and then press save (pressing save always takes you back to the original task list, not to the previous edit screen). Though some minor tweaks wouldn't hurt it, this app functions smoothly and has enough options to help you organize and stay on top of any to-do list.