>My understanding (such as it is) is that Tomcat supersedes Apache JServ,
>though I don't know how Enhydra compares with all this (despite quickly
>checking their web site).

JServ is an implementation of the Servlet 2.0 spec where Tomcat is an
implementation of the Servlet 2.2 Spec.  Tomcat also is necessary if you
want to use JSP, Java Server Pages.

Enhydra, as I understand it, is an application framework that separates the
data, the presentation and the business logic.  (MVC - Model-View-Controller
pattern).  It apparently has modules that help one define each part of the
MVC.  Without Enhydra or some other framework, one would have to develop
their own presentation scheme, data connection and business logic modules.
It seems one creates files that Enhydra converts into Java Objects.  As Java
Objects, there seems to be tools for rendering HTML, tracking state,
maintaining data, etc.

HTH,

Mark Wonsil
4M Enterprises, Inc.