Well, I would love to have this...
There are lots of music apps that set up playlists based on similar song characteristics...a la Pandora. I'm a big music fan, and I tend to categorize milestones, times of happiness, times of sadness, etc by the songs that I was into during those specific times. These memory-reviving songs are from multiple genres at times, so the Pandora method of picking tunes doesn't work for the app I'm imagining. Soooo, this app would take popular songs from a particular span of time...say the summer of '94 when I first went off to college and quickly found that college was, very, very fun. Ha ha ha. The app would play music from a specific memorable moment in time across all of the genres of music. You could pin different moments depending on what memory lane you wanted to revisit. I hope I explained this well enough.