The Really Bare Bones Board (RBBB) is a mini board designed for those experimental applications that require small processors, such as wearable computing, near space experiments, toy prototyping, artist’s projects or any use for a low-cost microcontroller.
The RBBB Pro is like a ready-made version of the RBBB kit, all tiny SMD components are already assembled - just solder in the headers and DC connector and you're ready to go. Unlike the original RBBB, no further soldering is required.
You'll also need a USB-to-serial connection, such as the USB BUB, to be able to upload sketches.
Remember that, like the Aurduino, this version uses 5v for chip supply and logic levels. There are 3.3V versions of this board available also - please contact order_assistance @ jee labs.org if you think you need the 3.3V version.
For further information about the RBBB Pro, see the official product page at Modern Device.
RBBB Pro's are shipped with OptiBoot 4.4, the same as used on Uno boards.