RS232 to FBUS adapter. This cable is used to talk to new units (eg. Nintendo Gameboy, and under-development ARM-based boards not yet in this webshop) that has no max232 chip onboard, only 3V serial (FBUS).
Btw, these are originally for different kind of mobile phones, most mobile phones have FBUS interface. Motorola, Nokia, Panasonic, Samsung, Ericsson ... etc. endless list. We usually cut down or unsolder the telephone-side connector (silly connectors :-), except the Motorola which has nice standard stereo 2.5mm jack. (if you'd like it to a particular mobile-phone, ask first if it's available, or if it's not a must, just a wish, write into the order note).