I use Kanka myself. I really enjoy it and love that it does what I need for free. I used to support it with a subscription when I had an active campaign going, but now that it's been dormant, I stopped. That said, I like that it's not necessary to do so to get a great tool for campaign building/management.
Other than that and WorldAnvil, the other big tool I've heard people use is a OneNote file. Not entirely sure how that works, but it's an interesting (and offline) way to do it.