Here's a completely rewritten "Arduino as ISP" sketch that can program the ATtiny85, in situ, on the Digispark board via its 6- and 3- pin connectors. It uses an Arduino Uno R3 as the programmer, and ...

This sketch can be used to let one Arduino program a sketch or bootloader into another one, using the ISP programming pins. This sketch is based on OptiLoader, but modified for use with Adafruit's ...