It's become a top-selling entertainment app for the iPad and iPhone and has been featured by Apple in its online store.

But for "Strange Rain," one question remains, even among those who have downloaded and enjoyed the application since it debuted last month.

What exactly is it?

"The easiest way to describe it is that it's a portable rainy day," said Erik Loyer, the app's Santa Clarita, California-based creator.

"Strange Rain" is a unique mashup of game, short story, easter-egg hunt and ... what? Meditation tool, maybe?

"It's almost like a David Lynch movie," said Mike Riley, a blogger who has reviewed mobile apps and features for more than a decade, referring to the director of mind-bending classics such as TV's "Twin Peaks" and the movies "Blue Velvet" and "Mulholland Drive."

In its most basic mode, "Strange Rain" depicts a stormy sky with raindrops spattering on the touchscreen. Tapping the screen in various combinations prompts music and, as the user progresses, more bizarre events.