It's... "closely coupled with a Xilinx FPGA. It's designed for users who care about Free Software and open source, and/or want to modify and extend their hardware: all the documentation for the PCBs is open and free to download, the entire OS is buildable from source, and it comes with a variety of features that facilitate rapid prototyping."

More than enough reasons for me. I'd buy one in a heartbeat, if I weren't broke right now.