While the results that many application developers have been seeing since the Facebook redesign launched last month have been mixed, some developers are finding ways to grow fast in the new Facebook world. One such developer is SocialCalendar.com, makers of the shared calendar and gifting app SocialCalendar.

In the last month, SocialCalendar’s monthly active users has nearly doubled – from 2.2 million at the end of September to nearly 3.9 million today. Why?

Raj Lalwani, CEO of SocialCalendar.com, says that growth can be attributed to:

1. The inherent virality of the application’s core functionality – adding friends’ birthdays (and other events) to your Social Calendar is a very natural use case that leads to application growth
2. The compelling context of the application’s emails and notifications – reminding users to send a message or give a gift to their friends when it’s their birthday or a national holiday works quite well

SocialCalendar’s growth shows that applications which provide new kinds of value to Facebook users can still achieve rapid growth in the new Facebook world. But the SocialCalendar developers admit that it takes a lot of work – the team of 3 in Silicon Valley’s Sunnyvale and 10 more employees in India say they couldn’t have gotten where they are today if they hadn’t been able to dedicate much of their efforts to developing full support for all the new and changing Facebook viral features.

SocialCalendar’s business plans call for pressing hard into gifting and gift cards, and the app has full integration with Amazon’s API for gift giving and wish lists. Soon, the company will make a natural move into high margin virtual gifts for users who wish to send pixels instead of physical goods – a business that Facebook has been doing very well in lately.

We’ll stay on top of SocialCalendar’s growth and other apps that are experiencing big shifts in traffic in the new Facebook world.