Sega Saturn de Hakken!! Tamagotchi Park, which featured cameos from many Sega characters.
One interesting point is that only certain eggs can become Sega characters, rather than one egg becoming any character (like the keychain pets). These "Segagotchi" eggs all have characters based on Sega hardware and franchises.
The baby and child characters are Master System cards, the teenage characters are a Saturn disc and a Mega Drive cartridge, and the adult characters are based on Opa Opa, Pengo, Flicky, Alex Kidd, and Sonic.
The games you can play include a food-eating contest (does Sonic eat chilli dogs?) and a Chao-style race, where you can cheer your pet on to make it faster.
The game as a whole sounds fun. If only Bandai would release Segagotchi in keychain form - that would be excellent!
[Source: WarOmnimon from Tama-Zone]