Remember The Milk
Remember The Milk (RTM) is similar to Evernote and Astrid. It's an online collaboration app that enables you to create tasks, assign priorities, due dates, times, create lists, use tags and more. The app syncs once a day with the Remember the Milk cloud server, and then your data can be accessed from virtually any Internet-connected device.
It was created with the goal of providing an easier way for folks to get things done---and it's effective for achieving that goal.