If you need a bare-bones, security-focused, micro computer, the USB Armory may be what you’re looking for. The differentiating feature is ARM’s TrustZone trusted execution environment on this USB stick computer i.MX53 processor.
The USB Armory is full-blown computer (800MHz ARM® processor, 512MB RAM) in a tiny form factor (65mm x 19mm x 6mm USB stick) designed from the ground up with information security applications in mind. Not only does the USB Armory have native support for many Linux distributions, it also has a completely open hardware design and a breakout prototyping header, making it a great platform on which to build other hardware.
Detailed talk from 31c3: