Hallelujah!!! Somebody has actually seen the thing!
I learned of this game back in 1999, at Gencon, and let it languish for 4 years, because while it is beautiful, and well-thought out, I assumed running a game like ths would be FAR too complicated to keep track of. However, it was through actual play that I realized the genious of this game: The players keep track of events, the GM doesn't need to!
To explain the whole precept of the game would take a very long time, but the basis is that time travel is a reality, and all of human history builds up to its creation. History consists of communities of time-spanners who work sentient force on the universe to ensure its existance.
All of its time-travellers live by 5 maxims:
1. INFORMATION IS ALL
Upon whether I know or not know a thing, depends my existence. If I know a thing is to happen, it is my foremost responsibility to see that it happens. This is my Yet, or Required Future, and it is the price I gladly pay to span time. Change of the known is resisted by the Continuum ceaselessly so that our greater liberties and lives will be fulfilled.
2. RESPECT YOUR ELDERS, THEY KNOW MORE THAN YOU
My elders, or Elder Selves, have been me, and more. I will show them every courtesy, and set aside anything I am engaged in to fulfill their requests. I will speak to them only when spoken to, like the well-mannered child of parents’ dreams.
3. MEASURE TWICE, CUT ONCE
Discipline is the lifeblood of the Continuum. I will know when and where I am and am going, and diligently record where I have been. I will arrange corners, or meeting places, when and where my fellow spanners can rendezvous in safety, and coordinate our actions.
4. INVITATIONS TO DANCE
If a Leveller, or other unfamiliar person witnesses a Spanning event, one of the following must obtain, in ascending order of rarity:
a)The witness is made to forget or never tell.
b)The witnessing was a strike against the Continuum; the witness is made to forget or never tell, and the parties responsible for the breach are sought out and brought down.
c)The witness is to become a spanner, like myself, a part of the Continuum and must be respected.
5. NEVER FIGHT FOR A LOST CAUSE
I will assist fellow members of the Continuum to fight their fragmentation up to a clearly defined point. Beyond that point I will no longer aid that spanner to repair their fragmentation. Lost Causes are spanners who, through accident or design, through their fault, the fault of others, or no fault of anyone’s, have suffered fragmentation beyond all aid, even their own. If such fragmentation ever afflicts me this severely, I will not hesitate to spend my remaining existence in assisting the Continuum.
The time-travelling community, or Spanners, live or dies by fragmentation, or Frag, in their lives, which is caused by other time-travellers, usually malicious, causing contradictions. Their existances are spent guarding against or curing Frag.
Past that, You'd really need the game to learn more. Below is a link to a story Hour I did that highlights the intoductory game that I used for two of my players. I based them in the 1980's, because it was one of my players' favorite decades (and T'pau being on of his favorite bands.

)
http://www.enworld.org/forums/showthread.php?t=50029&highlight=Continuum