Shazam was one of the first apps in the apple iPhone app store, and was also one of the first to make you think ‘whoa’. You held your phone up when any music was playing, and magically it figured out what song was playing and showed you the artist and title in seconds. Even 6 years later I am still amazed by Shazam compared to other apps that have come (and gone) since 2008. It did its magic by analyzing the digital fingerprint of a song and comparing it to its massive database of songs and more often than not, you got a result. It then saved a list of your results so you could download and buy the newly discovered song later. More recently it expanded to identifying TV as well.
There are a few copycats these days, including SoundHound, which improved on the concept by showing you song lyrics as well.
If you don’t have the Shazam app and have ever been in a restaurant, bar, store, hotel, or anywhere else music is played and wanted to know the name of a song, definitely download Shazam.