For all its flaws, Flash (or on of its incarnations like AIR or Flex) is still one of the few ways to create fully fledged desktop style applications that can be run in a web browser, mobile device, or as a traditional desktop application. By simply changing the target device when compiling, your code base can be used by almost any modern personal computing device without any significant changes.
The exception however, as announced by Adobe recently, is the Linux desktop.