Everything is PHP driven, and in the cases where it needs to store data (the keyword tracker for example), it uses MySQL as the database engine.
even for things like calculating the pagerank, you can do that through php? is it against google's TOS to do what you're doing and they just haven't noticed it? just curious
Not sure how PageRank is gathered, but that part is not done by me. Check #9 in the FAQ: http://www.digitalpoint.com/tools/keywords/faq.html