Several competing applications require running special software on the host computer, Briefcase doesn't. Mac users just turn on File Sharing in System Preferences and make sure that the iPhone and Mac are on the same Wi-Fi network. A list of machines appears on the iPhone, you tap on one to connect, and once the user of the computer allows you to have access, you can browse the directories of the machine you're connected to. WIndows and Linux machines simply need to support remote login via SSH. You can also make remote connections to machines if you know the IP address and SSH port number.
When Briefcase arrives in the App Store soon, it will cost US$4.99. A free version, Briefcase Lite, just lacks the ability to zap files to other iPhones. We'll write a full review soon. Until then, enjoy the gallery.