After development on RealmWorks was ended, I moved to World Anvil. It is a good and feature rich world building tool. It is pretty easy to get started with it, most of the difficulty has more to do with HOW you want to go about building your world, not so much how to use the tools. It allows you to export you content, so there is no lock-in, though it would still be a lot of work to take that exported content and put it in another system.
I ended up not continuing with my home brew world, but I keep my WA subscription for a long time because Frog God Games created a WA version of their Lost Lands setting. It was a great way to interact with setting content.
In short, if you are REALLY into world building and want a feature rich tool to do so that allows you to create interactive maps and cross-linked content pretty easily, with tools for sharing with your characters and tracking sessions, etc. I think WA is one of the best tools available. I'll also mention that if you use Foundry as your VTT, WA has a Foundry module to integrate your WA content into Foundry. I don't know if they have similar integrations with other VTTs.
I really liked the developer, who was very responsive to his customers and they put a lot of useful videos and help material to get you started. But I was worried about the fact that it was (at the time) pretty much one guy creating and supporting it. Maybe the team has grown. I don't know as I've not used it for a while.
Note that the reason I'm no longer a subscriber has nothing to do with the quality of the tool, I just didn't have time to home brew and wasn't really using it. If I were to go back to world building, WA would likely be the tool I would use.
