My favorite productivity tool is BusyCal.  I always have it open on my desktop and phone.  I really rely more on the reminders than the calendar events.  It syncs with iOS so if you're out and about and check a task as done it updates on all your devices.  Most of my reminders are recurring, so every Wednesday I know it's laundry day, that task automatically pops up every wednesday.  This app/software is a huge help to someone like me who's constantly forgetting all sorts of things :D