I have several:
House Organa Family Tree - I managed to decipher the tangled relations of the many, many Organa PCs that have been written on Chaos into a (more or less) cohesive family tree. Most of the characters were written by the same person, who is unfortunately no longer active, but they laid the groundwork which nearly all other writers have followed since.
House Khal/Hapan Royal Families - I had to go back to threads written a decade ago to learn the names of royal NPCs used in one-off threads, crafting a rough outline of descent down to the Daaray family. I did this just so that I could link my character Ben Khal's family to them.
Nimdok/Ike Family Tree - Probably my most prominent/high profile family tree, including
Sawa Ike
, her granddaughter Elise (writer appears to be no longer active?), Kyell Laysel (a character who used to be written by
Valery Noble
), and my own PCs.
Hoole/Harth Family Tree -
Inanna Harth
(née Hoole) and
Cato Harth
centric. Inanna can trace her lineage back to a canon character,
Mammon Hoole.
Dinn/Threepwood Family Tree - As you can probably tell by the crazy amount of children these two had, there used to be 5 writers active in this family. Now it's just me.
Those are the ones which involve more than one writer. I have a couple others that are just my characters, which I use for my own personal reference.
Kitter Bitters