Clannad is also a Visual Novel produced by the Key studio (also famous for the considerably more weird Air). It was released in Spring 2004 and has since been ported onto multiple console gaming systems, and has been adopted into multiple other mediums including manga, books, a film, and two anime series: Clannad and Clannad Afterstory, both produced by Kyoto animation.
Clannad in all its forms can semi-comfortably fall under the category of moe. It is melodramatic and character driven, similar in some ways to Haruhi or Toradora!. But Clannad is very blatantly harem oriented. While Tomoya Okazaki is not the most interesting character, he is the clear protagonist, and draws the constant attraction of all the other primary female characters. This creates different dynamics, advantages, and plot developments through Clannad's different mediums, but overall most of the characters are extremely likeable.
Clannad does have a reputation for unexpected moments of intense sadness for being moe, particularly as an anime. It is highly recommended viewing for anyone who enjoys slice of life anime, the works of Makoto Shinkai, or just anyone generally interested in crying manly man-tears.