Glassfish vs. Tomcat
Main DifferenceTomcat is merely an HTTP server and Java servlet container. Glassfish is full-blown Java EE application servers, including an EJB container and all the other features of that stack. Tomcat has a lighter memory footprint (~60-70 MB), while those Java EE servers weigh in at hundreds of megs. Tomcat is very popular for simple web applications, or applications using frameworks such as Spring that do not require a full Java EE server. Comparatively the administration of Tomcat server is more easier than administration of Glassfish as there are fewer moving parts in Tomcat.

Difference Between Glassfish and Tomcat
Glassfish vs. Tomcat
Tomcat is merely an HTTP server and Java servlet container. Glassfish is full-blown Java EE application servers, including an EJB container and all the other features of that stack.
Glassfish vs. Tomcat
Tomcat has a lighter memory footprint as compare to Glassfish.
Glassfish vs. Tomcat
Tomcat has footprint memory of 60-70 MB, while those Java EE servers weigh in at hundreds of Megs.
Glassfish vs. Tomcat
Tomcat is very popular for simple web applications as compare to Glassfish.
Glassfish vs. Tomcat
Comparatively the administration of Tomcat server is more easier than administration of Glassfish as there are fewer moving parts in Tomcat.
Glassfish vs. Tomcat
Both of the Tomcat and Glassfish are open source and free but have different licenses.
Glassfish vs. Tomcat
Glassfish is dual licensed while Tomcat has single license.
Glassfish vs. Tomcat
Tomcat uses the Apache License while Glassfish has been licensed under CDDL and GPL.
Glassfishnoun
Any of several unrelated small fish that have almost transparent bodies, especially those of the genera Ambassis or Chanda
Tomcatnoun
A tom, a male cat.
Tomcatverb
To prowl for sexual gratification.
Tomcatnoun
male cat
What is Glassfish?
Glassfish is full-blown Java EE application servers, including an EJB container and all the other features of that stack. It comes from the Oracle and thus each and every new spec will be tested and implemented with Glassfish first.
What is Tomcat?
Tomcat is merely an HTTP server and Java servlet container. It is run by Apache community. Tomcat is open source and free. It supports all Java EE technologies. It is not supported by any commercial support but only supported by community.