This schematic shows the Atmel AVR ATtiny24 circuit as it was built on the test board. The setup would be the same for the ATtiny84 or ATtiny44. The power supply is common and is shared between all of the microcontrollers on the board. Other than that, each microcontroller is in its own minimal circuit. The ATtiny24 is using its internal 8 MHz RC oscillator.
Here you can find the current ATtiny24 datasheet