Aye, its just a web-front end to mathematica. As to what Mathematica is written in - I'd assume C++. FORTRAN?

Webfront interacts with mathimatica via php? Only thing I could think of is like TCP/IP via ASP.Net but wolfram is no in ASP.Net and I don't know much beyond basic PHP.

Wolfram IS Mathematica. As to what they use on the front end to plug things from the web pages to Mathematica - I dunno. Doesn't really matter - anything could do it.