They are often more keen to tell us how beautiful their fonts are, than whether we can use them or not.
That goes not just for freeware sites, but also for commercial ones.
The websites are often rather vague on the subject, and not only because most of them are made for Windows and Unix users. The bad is that it is not easy to figure out which ones you can actually use. The good news is that there are lots of good fonts on the Internet provided for free, and more available commercially. With Arabic up and running on your Mac and programs to work in, the next step is to see what kind of Arabic fonts you can put onto it.
