(box art)
Tottoko Hamutaro: Tomodachi Daisakusen Dechu (とっとこハム太郎: ともだち大作戦でちゅ) for the Game Boy Color is the first game in the Hamtaro series. It was developed by Pax Softnica, published by Nintendo, and exclusively released in Japan. Despite being the 9th best-selling GBC game there, and well over 300,000 copies being sold according to Wikipedia, I own none of them, nor do I read Japanese, so that's about the extent of what I can tell you about this game.
Japan: September 8, 2000
The game is apparently a fortune-telling game. It resembles a pet simulation game in appearance, but you can't interact with Hamtaro, or take care of him. Rather, the player answers questions about themself, their family, and their friends, which the game then records in a digital notebook, and uses to generate fortunes. The game has a real-time internal clock, which triggers events in which Hamtaro speaks to you. It also has communicative functionality, that allows players to exchange notebook pages.
(nothing yet!)