It's during the holidays when I consider a "family" wiki. Imagine a wiki-pedia-like entries where family members can write different aspects of the family. An "entry" can be about a family member, an event, things (such as heirlooms, houses, etc.).
I think about the family history we have in our heads, grandparents, cousins, and long-forgotten relatives. Every family has some history... I think ours could be very interesting. Imagine the content that could be collected over the years (pictures, stories, etc.). We can look back and remember vacations, recall things about a relative we never knew directly. Also, the activities surrounding the writing and editing of entries can be good for the family as well.