Update: Well, that didn't last long! Apple pulled Floppy Cloud. Until next time, my friends.
Every year, Apple freezes iTunes and the App Store at the end of December, so the best time to sneak an app running a forbidden feature is right before December 22. This year, a $2 file management app called Floppy Cloud debuted conveniently close to the freeze so that Apple might not notice that the Floppy Cloud's definition of file management includes providing an expansive Super Nintendo and NES emulator, no jailbreak necessary.
Just looking at the app store, there's no indication that there's a hidden emulator feature. BUT THERE IS! And it's easy to use. After downloading the app, you can load a .nes NES ROM or .smc Super Nintendo ROM file using Dropbox. That's it: Floppy Cloud will play it. The app also supports both iCade and MFi controllers.
This is becoming something of a Christmas tradition. In the past, apps like iMAME and Gridlee have popped up to let iPhone users get a taste of un-jailbroken emulator fun.
Screenshot via TouchArcade