Decks is a casual DJ app for the iPhone that lets you play with a series of tracks and mix them together.
This free version comes with seven short tracks that you can load into on-screen decks and mix between. The horizontal interface shows two record decks, below a colorful display of records. Touch one of the records, and drag it to a deck and it will load and play. Touching that deck will stop and start the track.
Load a track into the other deck, and it will automatically sync with the first, so you can use the crossfader in the centre to flick between the two. The automatic syncing means you don't have to worry about beat matching, and almost whatever you do will sound fine!
This is very much a toy application, but it's pretty fun even though the small number of very short tracks means it gets repetitive after a while. It's also a shame you can't scratch with the record decks, as it feels like you should be able to!
If you want a fun app that allows you to feel like a DJ, Decks will let you feel like you've got the skills to rock the party.