May be mind maps https://whimsical.com/mind-maps. Source: over 2 years ago

When you said hopefully to include player campaign notes, I thought of kanka. It's somewhat less feature-rich, I think, but it is potentially-free and collaborative. Source: almost 2 years ago

Our group has been using Kanka (https://kanka.io/en) for the past few years and it’s been super helpful. Source: almost 2 years ago

Some people I know have recommended kanka: https://kanka.io/en. Source: about 2 years ago

I use Kanka, I’ve found it to be excellent. A few key points: - there are loads of different page types you can create, characters, locations, organisations, items, it’s quite varied. Although you can’t make custom ones I’ve never needed to. - you can easily link to other pages within your Kanka campaign by typing and @ followed by the name of the page, so @Barry will pop up a list for you to select from your... Source: over 2 years ago

I've also heard some pretty good things about Kanka (https://kanka.io/en), though I haven't tried it myself yet. Source: over 2 years ago