QuickBooks SDK 

QuickBooks SDK allows you to develop desktop applications that integrate with QuickBooks Desktop, the most common small business accounting platform. With the program, the small-business owner no longer needs to enter the same data twice. Because the application can share and modify QuickBooks data, the small-business owner has the best of both worlds, the power, ease, and comprehensiveness of QuickBooks combined with the benefits of an application tailored to the unique needs of a particular small-business concern.