This schematic shows the ATtiny13 circuit as it was built on the test board. 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 ATtiny13 is using its internal 9.6 MHz RC oscillator, which divided by 8 gives a 1.2 MHz system clock. With 1kB flash and 64 bytes of RAM, the ATtiny13 is one tiny ATtiny.
Here you can find the current ATtiny13 datasheet