Tomcat is designed to be a fast and efficient implementation of the Servlet Specification. Tomcat came about as the reference implementation of this specification, and has remained rigorous in adhering to the specification. At the same time, significant attention has been paid to Tomcat's performance and it is now on par with other servlet containers, including commercial ones.
In recent releases of Tomcat, mostly starting with Tomcat 5, we have begun efforts to make more aspects of Tomcat manageable via JMX. In addition, the Manager and Admin webapps have been greatly enhanced and improved. Manageability is a primary area of concern for us as the product matures and the specification becomes more stable.