djay for iPad is not a remote. It's a freestanding deck with two turntables, a crossfader and all of the music on your iPad. Throw a record on a turntable (I mean, click the "add track" button and pick a song from your iPod library), and it immediately grabs the end time and starts building a waveform and measuring BPM as it plays. There's a wait time for the analysis, but it usually wraps up in the background before you'd need to do anything with the info. It will also remember tracks it has already analyzed the next time you use them. It even remembers cue points that you set on a track between loads. You can spin the records forward and backward, scratch and there are realistic simulations of braking and backspins. Optionally, it can add tape markers to help with cueing, and the waveform display above the table zooms in when you're spinning or scrubbing so that you can target beats visually.
Sliders at the top let you adjust the gain for each table individually. Sliders on the left and right let you set the speed, increment and decrement it manually, or sync one table to the other automatically (within about a 10 percent BPM difference). If you have a mono/stereo headphone adapter, you can pre-cue in your headphones while the main mix is sent independently to your speakers. Add a crossfader (which it has, obviously), and you've got a pretty complete simulation of an actual deck. It doesn't feel the same, but with a little practice, it can compete.
The Automix feature can be a lifesaver. If you want to, you can just cue up a playlist and leave djay running all night, without ever having to touch it. You can set the transition style to Standard, Backspin, Brake or Reverse, or just set it to Random and let it seem like you're being creative the whole time. It's not brilliant about customizing the syncing and crossfades, and it starts transitions at a set time-remaining, which works better on some transitions than others. While it won't replace the musical ingenuity of a human DJ, it will make any playlist a lot more fun and keep the crowd dancing. You can record a set ahead of time, too, and sync it to your Mac or PC with iTunes.
djay uses a lot of memory, what with the track-by-track waveform and BPM analysis. If you're planning to run the music at a party with it, I suggest you restart your iPad first to free up as much memory as possible.
If you give it enough breathing room, djay for iPad will rock that party. You can read more at algorridim's site, or head straight for the App Store (US$19.99).