if possible please don't use Adobe AIR anymore, it's a really shitty VM and the old downloader was full of bugs, even java would be a better choice
I lol'd, really. Anybody who used any java based downloader knows how slow this crap is.
I know but it's better than AIR! And I hate Java :)
The best choice would be of course a little C++ client, even C# would be better but I suppose they could not want .net dependencies.
Adobe AIR is basically stand-alone Flash. And believe me that Flash virtual machine is even worse than the JVM.
It has a shitty, bugged, garbage collector and the runtime itself is very prone to bugs