I particularly like https://en.wikipedia.org/wiki/Marefa. I wouldn't know about the quality of the content - I don't speak Arabic - but from what I can tell it's like Arabic Wikipedia, but you also get blogs, forums, ancient manuscripts, email with unlimited storage (?!?) and much more. The Arabic internet in general is always interesting to me, because even in 2021 it still seems very ad-hoc and far less commercialized than the parts of the internet I've seen in other languages.
