I was playing Tik Zak Toe last night. It's basically a way to look at relationships of things in a game. Go read it. I'll wait.
While Zak initially aimed it at creating adventures, I began to think of another use (ed. or rather, I just checked and he mentioned this use too) - that of charting out relationships between entities in a campaign - kind of a record of adventures already gone by. The things that go on between players and npcs can get messy and confusing in a long campaign, and the matrix is useful for examining those relationships.
Here is one I worked out last night for the Tales of the Razing Zone campaign I am running:
It's a fun exercise and got my head cleared up about some things, like how the Sorceress had never met Ferrit, but had put a price on his head. That's good to remember when and if they finally meet. I screw up things like that in campaigns. Little details. It's a neat tool.