Atmel ATTiny core taken from https://code.google.com/archive/p/arduino-tiny/:
Arduino-Tiny is an open source set of ATtiny "cores" for the Arduino platform.
The Arduino platform currently supports Atmel ATmega processors. There is a need for the Arduino platform to work with physically smaller DIP package processors. The intent of this project is fulfill that need. Specifically, our goal is to provide a core that enables Arduino users to work with the ATtiny84 (84/44/24), ATtiny85 (85/45/25), and ATtiny2313 processors.
For more information about Arduino, see the website at: http://www.arduino.cc/
CREDITS
Arduino is an open source project, supported by many.
The Arduino team is composed of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David A. Mellis.
Arduino uses the GNU avr-gcc toolchain, avrdude, avr-libc, and code from Processing and Wiring.
Arduino-Tiny is based on work by David A. Mellis, Ren Bohne, R. Wiersma, Alessandro Saporetti, and Brian Cook.