Tomcat is one of the oldest members of the Apache family, and one of the standard building blocks of the web as we know it today. It can sometimes fall below the radar, because it just works, so most folks are completely unaware of it.
Filip Hanik will be doing a training class on Tomcat at ApacheCon this year. I spoke with him last week for Feathercast, and I’ve finally edited it. You can listen here, or come to ApacheCon and hear him there.