A few weeks ago, I pulled off a major feat for a fortysomething relic in the company of a 15-year-old. I taught him something cool about his phone.

After my friend’s son, Davis, described the advantages of his Droid X, he came to its “one big downside.”

“I can’t get my iTunes music on it,” he said.

“I’ve got an app for you,” I said. “DoubleTwist.”

He looked it up on his phone. “Wow,” he said. “That’s it.”

DoubleTwist, which is free, gives people a way to easily sync their iTunes music library with their Android phones. As such, it’s one of the most important, yet often overlooked, pieces of software on the Android market.