We happened to write the frontend in PHP. Hey, it was 2006, and we were high school students ;-)
Picked 'by default', Apache is actually serving the content.
Aside from usual web UI stuff, the user support widget/chat client, Z-XMPP, is written in it.
Most of the data in ZATEMAS is stored in MySQL.
Our online judge, 'Evaluator', is written in it.