hi, rob , for the question, what is tomcat,
you should refer to
link and why people using tomcat is of course it is free as major factor, some other reasons like stability , easy to use ..it did a very good job considering if you only want to use tomcat for
jsp and
servlet processing, it running is light weight as compare with
j2EE application server which consist other components that you may not need..
further points like supported and intergrated with major
IDE , finally, it is extensible if you want to plugin some nice framework like
struts