The World Forge
The basic idea is that each player takes on the role of a scholar, from before scholarly pursuits became professionalized (or possibly after they ceased to be). You are cranky, opinionated, prejudiced and eccentric. You are also collaborating with a number of your peers — the other players — on the construction of an encyclopedia describing some historical period (Ananda's decent into the Underworld and revelation from the Wheel of Fate of the False World of Spirits, the Great Lie of the gods, & the True World of Matter).
The game is played in 26 turns, one for each letter of the alphabet. Each turn will last 1 fortnight (of real time). This is a low key world building game
1. On the first turn, each player writes an entry for the letter 'A'. You come up with the name of the entry, and you write 100-200 words on the subject. At the end of the article, you sign your name, and make two citations to other entries in the encyclopedia. These citations will be phantoms — their names exist, but their content will get filled in only on the appropriate turn. No letter can have more entries than the number of players, either, so all citations made on the first turn have to start with non-A letters.
2. On the second and subsequent turns, you continue to write entries for B, C, D and so on. However, you need to make three citations. One must be a reference to an already-written entry, and two must be to unwritten entries. (On the 25th and 26th turns, you only need to cite one and zero phantom entries, respectively, because there won't be enough phantom entries, otherwise.)
It's an academic sin to cite yourself, you can never cite an entry you've written. (OOC, this forces the players to intermingle their entries, so that everybody depends on everyone else's facts.) Incidentally, once you run out of empty slots, obviously you can only cite the phantom slots.
3. Despite the fact that your peers are self-important, narrow-minded dunderheads, they are honest scholars. No matter how strained their interpretations are, their facts are accurate as historical research can make them. So if you cite an entry, you have to treat its factual content as true! (Though you can argue vociferously with the interpretation and introduce new facts that shade the interpretation.)
4. This little game will probably play best on a wiki, and it should take a month or so to play to completion. At the end of it, you'll have a highly-hyperlinked document that details a nice little piece of collaborative world-building.
The general subject of the Lexicon: You are all revisionist scholars several hundred years separated from Ananda's decent into the underworld and revelation from the Wheel of Fate of the False World of Spirits, the great Lie of the Gods, & the true world of Matter.