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. 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.

Key Differences
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.
Tomcat is very popular for simple web applications as compare to Glassfish.

Aimie Carlson
Jan 03, 2016
Tomcat has footprint memory of 60-70 MB, while those Java EE servers weigh in at hundreds of Megs.
Tomcat uses the Apache License while Glassfish has been licensed under CDDL and GPL.

Janet White
Jan 03, 2016
Tomcat has a lighter memory footprint as compare to Glassfish.
Both of the Tomcat and Glassfish are open source and free but have different licenses.

Harlon Moss
Jan 03, 2016
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Comparatively the administration of Tomcat server is more easier than administration of Glassfish as there are fewer moving parts in Tomcat.
Glassfish is dual licensed while Tomcat has single license.
Glassfish and Tomcat Definitions
Glassfish
Any of various small, semitransparent fishes of the family Ambassidae, found in marine and freshwater habitats of Africa, Asia, and Oceania and often kept in home aquariums.
Tomcat
A male cat.
Glassfish
Any of several not closely related small fish that have almost transparent bodies, especially those of the genera Ambassis or Chanda
Tomcat
To be sexually active with more than one partner. Used of men.
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Tomcat
A tom, an intact male cat.
Tomcat
To prowl for sexual gratification.
Tomcat
A male cat, especially when full grown or of large size.
Tomcat
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.