This is a very good website in Arabic language which is like an online magazine, it posts articles in many domains and fields; social, environmental, technological, mathematics, physics, biology, philosophy, and psychology.
Adding the best online magazine in your own language in comments is most welcomed.
Have a good day.
after surfing this website, I think it is pretty difficult for Arabic learner to read and improve the reading skills. Just the advanced learner may challenge the new vocabulary and the complicated structures. I see the materials included in the website are mostly academic topics more than general. It is just a perspective to teach your language partner. Generally, I wish I could find such as this web site in english, that might be helpful for IBT practice.
@Michaela if you learn standard Arabic you will find all articles suitable for you, and in general most of Arabic articles on such sites are not in a specific dialect but standard Arabic "Fusha".
For people learning an Arabic dialect, reading can be more difficult because it's harder to find materials in the dialect we are learning.