arduino is open hardware?

Projects Discussion and Showcase Device Hacking
1

i came across this post in the raspberry pi forum:
http://www.raspberrypi.org/forums/viewtopic.php?t=55777&p=422729

so i would like to know of the documentation for hardware of the arduino is available for the general public, namely the documentation of the chip.

i thank you in advance for the answer

2

Did you want the ATmega328P datasheet?

http://www.atmel.com/Images/Atmel-8271-8-bit-AVR-Microcontroller-ATmega48A-48PA-88A-88PA-168A-168PA-328-328P_datasheet_Complete.pdf

Or did you mean something else?