Think of it as an Arduino for security. I can be programmed to act like a U2F token, a bitcoin wallet, secure storage for ssh keys, etc. A future version will have a second USB port so it can turn a regular USB thumb drive into an encrypted drive, act as a "USB condom" between your computer and a suspect USB device, or turn a regular keyboard into a smart keyboard that can generate and play back secure passwords. Because it has local I/O (a display and two buttons) it can do all of these things while remaining secure against an adversary that pwns the machine it is plugged in to. And because it uses stock hardware and is user-programmable you can be fairly confident that it doesn't have any back doors built in to it.

Of course, it doens't actually do most of those things yet (working on getting the bugs out of the U2F code right now) which is why right now it's just a toy for hackers and devs. But the apps are coming.