QLab is a great Mac application for producing live audio and video shows.
Who needs QLab…
Anyone who is frustrated by trying to use Keynote, Powerpoint, DVD Player, Adobe Director or even iTunes to control what people see and hear at live events. Whist Keynote & Powerpoint will both handle audio & video they become a bit unwieldy when under the time pressure of live shows. They don't offer tools like mixing multiple audio/ video tracks at any point in time or creating loops that break out when you want. Removing or adding items is not something I'd be willing to do 20 minutes before an event starts, but QLab changes all that.
What you will need...

With the Mac community currently caught up in the seemingly endless hype and speculation surrounding the iPhone, it is easy to forget that there are other smartphones out there that have been providing all the same functionality that the iPhone provides, and a whole lot more, for the last few years.
Well it seems the iPhone is a resounding success. Loads of them have shipped and with the new development opportunities opening up from apple (see iPhone developer site) things can only get better.