I have been playing with World Anvil - essentially it’s a specialised Wiki-like tool for designing and documenting world settings for RPGs and the like - things like timelines make it great for this. .
I’m using it for my D&D world (and as such the main review will go in The Sage DM) but I’ve also just started using it to manage the complex background for Secret Project C (which is a setting for TFL’s Quadrant 13). Very impressed. More later.