Rejoice, fellow Backpack users, for 37Signals today added a much-requested new feature for paid users: a calendar. As you may come to expect from the traditional KISS approach of 37Signals, the calendar is incredibly easy to use and enter appointments into. It's also 'smart', as it can figure out what events like "January 7 Catherine's birthday" and "6:30pm Dinner" mean, and it will place them where they need to go. Users can also create multiple calendars and assign unique colors to each, and events are pleasantly drag-and-drop-able between days. Unlike Google Calendar, this Backpack Calendar can remind you of events no matter which calendar they are entered into, however the reminders (at least for now) are set at a static 30 minutes before the event. Calendars are also shareable and subscribe-able via the iCal format, and just as with Backpack pages, calendar addresses are able to be reset, should you find a need to stop sharing one down the road. The one thing I haven't tested yet is whether this calendar has any kind of accessibility via Backpack mobile. If you try this out, sound off.

As a paid Backpack user (just the Basic $5 plan), I have to say: I am pleased. I retreated from using Google Calendar a little while ago, in part because of the silly limit of only being able to receive reminders for events in the Personal calendar, and no others. Plus, this is another great reason to start using my Backpack account even more, especially since I've found a killer offline Backpack client by the name of Packrat, which I've blogged on TUAW. One downer that I can see from this new calendar being a paid-only feature, however, is that (as far as I know) free account users don't have any way of testing it out. I guess freeloaders (just kidding) could spend the $5 to 'temporarily' upgrade and test it out, then simply downgrade if they aren't happy. Ultimately, I think this calendar feature is almost worth the $5 alone for any Backpack user looking for a little more organization in their lives.