I recently heard about a new site that just started operating this year.
It's called Books on Track:
https://booksontrack.net
It doesn't have every bit of functionality that FictFact did, but it is much better than any other suggested replacement I've seen. I exported my data from Goodreads and was able to import it in a fairly decent state (some review cleanup was necessary). Since the site is new, there are missing books/series, but it is very easy to report/suggest missing information.
There's a thread on Goodreads about it, and the developer is pretty prompt about responses.