WiiFree
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WiiFree Info
WiiFree is an open-source PIC based modchip.
Only one chip with 8 pins is used (5 pins to solder). It can be the PIC12F629 or PIC12F675 from Microchip. These chips are cheap (about 5$) and easy to flash and a lot of information (including the .hex file) is provided in the forum linked below. Simple programmers cost less than 10$.