Mac OS X: CalendarBar is a really handy menubar utility that stores your calendars in your Mac OS X menubar. It syncs up with Google Calendar, works with iCal and even Facebook.
When you launch CalendarBar for the first time, you'll be asked to set up your various accounts. You can just check a box to display iCal easily, but you can also log in to your Google and Facebook accounts to sync events with both. Facebook will require the usual app authorisation but Google will only require credentials. Once you're in you'll see the next week or two available in your menu bar, colour-coded just like in the actual apps. Clicking an item will take you to that calendar item so you can view or edit it. It would be really nice if you could quickly add a calendar item directly from the menu, but nonetheless CalendarBar is a handy way to access your calendars with just a click.
CalendarBar ($2.49) [Mac App Store]