Installing additional Arduino Cores
https://www.arduino.cc/en/Guide/Cores

Unofficial list of 3rd party boards support urls
https://github.com/arduino/Arduino/wiki/Unofficial-list-of-3rd-party-boards-support-urls

Informationen zur Installation von Libraries finden sich unter: 
http://arduino.cc/en/Guide/Libraries


Unbedingt lesen, wenn man was mit ATtiny machen will!
Programming an ATtiny w/ Arduino 1.6 (or 1.0)
http://highlowtech.org/?p=1695