Velocity:
Velocity is a general purpose Java-based template engine.
Suitable for many application domains including source code 
generation and XML transformation and styling, it is most 
often used in J2EE web applications as the view layer for 
generating dynamic content.

Tomcat:
Tomcat 4 is the official Reference Implementation of the
Servlet 2.3 and JavaServer Pages 1.2 technologies.

links:
http://jakarta.apache.org/tomcat/index.html
http://jakarta.apache.org/velocity/index.html
http://java.sun.com/products/jsp/index.html
http://java.sun.com/products/servlet/index.html
http://www.acm.org/crossroads/espanol/xrds8-2/servletsProgramming.html