"Dekstasy" has been around for quite some time, and hasn't seen any development since last year. That said, this app is very very useful, although I can't say its easy to use. It allows a DJ to perfectly beat-match mp3's and other music files. It has a rudimentary fx processor, and is capable of seamless looping.
For instance, it has a tabbed interface. It would benefit, instead, from multiple windows - the mixer/fx are on one tab, while the cueing, looping, and bpm controls are on others. This makes it painful to use, impacting the agility of a performer. That said, it can almost flawlessly sped up and slow down music without it sounding like its dragging or "chipmunked."