"It's the open I/O specifications that make Arduino different
from previous board coalitions. The connectors are exposed and
fully documented, so that amateurs can link the Arduino CPU to
purpose-built add-on modules called 'shields.' By placing hardware
details and the Arduino language within the Creative Commons
licensing program, the Arduino movement encourages sharing and
innovation among hardware hobbyists in the same way Linux
encouraged growth of open applications.
"The program already has grown beyond the boundaries of an AVR
CPU, with at least two companies offering ARM CPUs, and another
offering modules based on the Microchip PIC family."