Azendoo allows you to define when work on a task should start or simply to snooze it for a while.
By default a task is considered as To-Do, meaning you can work on it already (though you may not fully complete it today and may work multiple times on it, with other participants, etc.)
Then, if you cannot work on the task until a specific date, or just want to plan a project in advance, you can use the Plan for later button
If a task no longer needs to get done but you don't want to delete it for now, you can mark it as Canceled using the 3d button. These task can be reactivated anytime.
The task will be listed in the Canceled lists and be displayed using striked-through text.
Of course once the task is completed you can mark it as done (and also as undone if needed)
Due date and reminder
In addition to planning a task, you can set a due date and add a reminder for the assignee : http://help.azendoo.com/tasks/collaborating-in-tasks/due-dates-and-reminders