Released for the Game Boy Color on October 18, 2001. This cartridge is designed to turn the Game Boy Color handheld into a child-friendly personal digital assistant. The E.T.: Digital Planner features an address book, a calendar, a clock, and a "To-Do" list, all presented in a theme inspired by the hugely popular 1982 film. The software also contains five mini games, including the opportunity to care for a "Flopgopple" virtual pet. Kids can protect their personal information with a password or print it out on the Nintendo Game Boy Printer.
Source: Wikipedia, "E.T. Digital Companion", available under the CC-BY-SA License.