You don't need an app at all. Simply connect the Nexus 7 to your computer and drag whatever audio files you want into the "Alarms" folder. They will then show up in the clock app.
Originally Posted by Esot-eric: “You don't need an app at all. Simply connect the Nexus 7 to your computer and drag whatever audio files you want into the "Alarms" folder. They will then show up in the clock app.”