The guy you are replying to was employee 2 or 3 depending on how you count at Amazon.

There was a ton of various scripts written in perl that kept everything running for sure. The website code was C/C++ as mentioned elsewhere.

In 1999, front end templates were written in an internally developed macro language named catsubst and served by a C (maybe C++?) application named Obidos. Later (starting in 2003-ish), front end code was written in Perl (Mason) and served by another application named Gurupa. The transition to Gurupa was very long and arduous. I've no idea how the site works now.

Calling it an "internally developed macro language" is stretching it a little bit. It was an extremely simple blob of C++ code that scanned text looking for one of a very small number of known placeholders, and filled them in with the relevant value (session ID, user name, user email etc.) I suppose that over the years between 1996, the capabilities of catsubst may have been expanded somewhat, but certainly when it started there was no formal concept of it being a macro language. In fact, at the very beginning, we experimented with just using m4 (which is a formal macro language) but it wasn't quite right for the job.

Fair enough. I maybe should have put language in scare quotes. :)

The transition from Gurupa to Java (Spring, Horizonte) was long and arduous. If you see a page with /b/ in the url, that's Gurupa.