Astrid may look unassuming when you first encounter it, but the free, open source task and to-do list-maker has customization settings beneath its skin. Type to add a new task. You can leave the note to self where it is, or select the entry to edit elements like importance settings, tags, notes, deadlines, recurring reminders, and alerts. We like being able to add tasks to
's calendar, and that there's an option to sync with online reminder service Remember the Milk.