The concept: two players, one an archaeologist, the other a member of a long dead civilization. The archaeologist discovers a journal written by the long dead person while investigating the ruins of the city. The player playing the dead person writes about their life, detailing places while leading up to whatever caused the cataclysm. The archaeologist writes about how the place looks now. I think the idea was that either one could introduce elements that the other would then talk about in their own time. Like the future person might talk about a colliseum with a huge pit in the middle of it, and the past person would then maybe explain how that pit got there, that kind of thing.
The mechanics: I can remember something about white and black stones. I think they were used to say who owed who something (like if the past person is supposed to follow up on something the future person introduced), and also to figure out how far from endgame they were (like after a certain number of stones were used, the cataclysm arrives).
That's all I remember. I'm pretty sure it's a half-baked game sitting somewhere on the net. I'm pretty sure I found the link for it somewhere on story-games, sometime in the past. Any help finding this game would be cool.