What is Raspberry Pi? No, I didn’t make a spelling mistake, just take a look at this
It is a USB-powered, credit card-sized computer that comes with a network connection port, one or two USB ports ( model A or B ), HDMI out, composite RCA video and 3.5mm audio out, SD card slot, camera slot and up to 25 GPIO pins for various applications.
You can also check out this page:
See also:
http://www.raspberrypi.org/
https://www.modmypi.com/