AVR-Chat

> I have inadvertently bricked an ATTINY13 after trying to set the fuses.

Well you may have:

1) Set the AVRs clock to be too slow for the SPI clock speed in your ICSP.
Try slowing your ICSP programmer speed right down.

2) you've enabled the external xtal/clock so it will now need some sort of
clock signal on that pin, while you revive it by setting the fuses with a
ICSP Programmer back to what you need.

HTH

Alex