Mathematics Illuminated

I just chanced upon this interesting site – looks like it might be useful on the diploma course.
There is a lot of mathematics theory, split into 13 subject areas including primes, infinity; topology; geometry, and much more. Plus a useful ‘Math Family Tree’ which look at the history of the 13 subject areas and “illustrates how early mathematicians and their breakthroughs (as far back as 25,000 B.C.E.) influenced those that came later”.