What technology would be best for developing a robust, pro quality game launcher?

I need it to update the game using some kind of P2P protocol. I also want it to look exactly the same on all desktop platforms: Windows, Linux and Mac (custom window frames and custom GUI).

I thought about Adobe AIR, Java and Qt Framework. Is there anything else viable? Which of the three would be best? I have experience with AS3, Java and C++, so language is not a barrier. It's more about the requirements and speed of development.

I vote Qt - I don't know of anything better for cross platform GUI dev especially if your already familiar with c++

There also is Lazarus IDE and LCL. It's open source clone of Delphi and VCL. It's a Free Pascal toolkit, has a good feature set, can call C libraries easily via the use of h2pas tool and has backends for a lot of GUI toolkits (GTK 1, 2, 3, Qt 4 and some custom pascal only ones and native ones, in various stages of completion).