Jonas Norberg built two great products that nobody used. The first was the award-winning Pacemaker, a wonderfully nerdy beatmaking gadget that cost $850. The second was a tablet app for DJing, but Norberg chose the wrong partner to launch with — the BlackBerry Playbook. After being booted out of his own company and then buying it back, Norberg is trying once again to make a dent in the world — but this time, he picked a better partner: Spotify. Pacemaker for iPad, a new DJ app, launches today with exclusive access to Spotify's massive streaming music library, and the ability to play two Spotify songs simultaneously for the first time.