It's a zip file following Java convention that can be dropped in any Java web application server (like Apache Tomcat).
Basically a lot of sites you go to have been deployed by dropping a .war file in a Java web application server. That technologically powers a gigantic part of the Internet (just look at SO or Quora or expert exchange or any TIOOBE index or any Java job offer: Java webapps are pretty much powering the Real-World [TM]).
Having no idea what the software stack is, and only basing a guess on having read plenty of Joel's musings, I'm guessing a Microsoft technology. I'm sure someone has the goods, or Google could probably answer.
I think he is suggesting that the number of java related questions on those sites indicates the language is widely used. Neither SO or quora run on java.
Basically a lot of sites you go to have been deployed by dropping a .war file in a Java web application server. That technologically powers a gigantic part of the Internet (just look at SO or Quora or expert exchange or any TIOOBE index or any Java job offer: Java webapps are pretty much powering the Real-World [TM]).