Onlytasks is a simple task organizer that allows you to create to-do lists very easily. The lists can be easily arranged by category in the so-called "Notebooks". The notebooks can contain multiple tasks and you can assign them a name, a tag (that's customizable), due date, and you can write a short description for all of them. The application also has a calendar, so you can easily view the tasks by day and even by status. For instance, you can view those that are overdue, those tasks for today, tomorrow, next 7 days, without a due day, etc. There's also a search dialogue, so you can search for tasks by entering a keyword.
The tasks marked as done will remain on your notebook, but won't appear in the calendar or in the status panel. A great thing is that you can send the tasks to iCal, so you can also have them there. This is great because Onlytasks doesn't include reminders or alarms, which is a feature present in iCal. The program offers a neat, simple, and very attractive user interface that won't cause any trouble.
Thus, if you are looking for a simple task organizer for you daily life, Onlytasks can be a good choice.