You probably got used to Arduino and know very well how standard Arduino board looks like. Well this one is a bit more different. This Arduino actually is software based and runs inside FPGA. Running soft processors in FPGA isn’t a new thing – you can find soft AVR8 microcontroller in opencores.org.
So what is a benefit of running an Arduino of FPGA? Well remember that FPGA is very flexible and fast platform so virtually there is no limits in prototyping… if there are no analog signals included. Anything else including UART, PWM, Timers, interrupts are working fine. Soft processor can be customized to have more I/Os or more peripherals like more PWM channels. Clock speed can be also higher that in standard Arduino. They actually modified Arduino IDE a bit to fit soft processor requirements, but you get same feel on writing sketches like for regular ones. I think running just Arduino on FPGA isn’t very effective way, but think about bigger scale project where soft processor is a small part of it. Because of programming simplicity and lots of open source resources it may be much easier to do some routine tasks in Arduino style.