I'm not sure if there is another thread like this, but since this is something SubRosa did tackle a bit, I would share this online tools I personaly find useful.
kumu.io/ is a tool with which you can very easily make relationship charts. It's a tool I use now from almost 1 year and a half, and I find it very interesting. You can have elements typed (in my own chart, I have for example: 'persons', 'organizations', 'factions') and connections between those typed (in my own chart I use: 'neutral', 'positive', 'negative', 'favor', 'family', 'alias', 'member',).
You can have one or two (easy) connections between two elements, but you can create more. For example I have two npc with those three connections (to prevent spoilers I'll use anonymity):
A loves B, friendly type connection
B hates A, hostile type connection
A and B are brother, family type connection
For each element or connection, you can have a "title" or "name". EG: 'Darius' or 'Murion', or for a connection between an ex member of your PC covenant 'was member up to [date]'
You can then add tags. For example, for every "element" typed as 'person', I have one of those: "magus", "mundane", "surnatural creature".
EG: a main NPC such as "the pope" could be tagged with this: 'mundane', 'priest', 'pope', 'tribunal of Rome'
You can hide and show any elements : all, none, typed X, typed X but not Y, etc, and/or connections (although you cannot show connections without showing the elements the connection refers to, which is quite logical but would be fun to watch).
You can then assign size properties. EG: "all the tag 'major' should be +150% sized.
Obviously, being a relationship chart, you are able to zoom out (see the big picture) or zoom in (see the micro details of the relationships).
Each element can have a description with formatting and ability to use hyperlink.
Each element can have an image.
And you can save "views", which are in short a partial view on your relationship chart, based on criters. For example you could create a view called "the Order" mapping the Order of Hermès", or another view called "the foes" to map the relationships between the foes of your saga.
Obviously, you must have at least one view (which is simply "all your relationship in one screen" ^^) but need not work on the big picture everytime.
You can make powerpoint like presentations if needed (which I did for the provençal tribunal my RL group has joined since march 2016). (You can view it here (texts are in french sorry). - It shows you what I was able to do after only 1 week with the tool. I have been getting better with time.)
You can make "export", and import of excel or google drive tables to quickly add a lot of items in one go, if needed.
As for now, I personaly have something like 500 elements and 900 connection in my own saga chart.
One of the thing I find lacking is the possibilty to add something of a time factor, because sometimes I want to say:
1250 : A => B: friend of (type: friendly)
1260 : A => B: ennemy of (type: hostile)
1261 : A => B: has killed (type: hostile)
and withtout a timestamp thing, I can only put all those in the description of one connection, but then I face the issue: which type should that connection be? friendly or hostile? or neutral to sum those two?
It's a timeline tool I discovered 2 weeks ago.
I find it very useful in principle (even if I have not yet used it for a saga). With it you can create events for peoples and adventures, and see how logical they each follow.
I think that those two tools combined offer a really interessant approach to the adventure creation process, and keeping track of NPCs activites which are important for your setting credibility.
I will try it for the first time with my current mega adventure (encompassing 2-3 years in game, but worth 3 to 5 adventures which each will take 1 to 3 sessions to complete), because the coherent nature of the world is one of the most important thing for me when I create an adventure. I want the players to think that there is a logical explanation for every decision an important NPC take, which means I must know why they are deciding, which factor explains what they did know, or what they wrongly knew at the time of decision. The web of those NPCs actions creates the background, and the events which happen during gametime, and those will happen (modified or not if the PC act to prevent/aid them).
Apparently on one timeline you can add events at any moment (1200+ is available, which was important for me since... Ars magica ^^) and decide a size factor, within the zoom levels. Biggest events can be seen from the big picture (century? millenia view), lowest events are seen from close (EG month or week) and invisible from above.
My dream tool would be a fusion of both of those: timeline + event with relationship evolving through time.
But I guess that would be a visible mess (because 3D at least) and a hell to create.
And you, do you have any useful tool you use?