Why use Glassfish instead of Apache? What’s it strengths and weaknesses?

GlassFish is an Application Server which can also be used as a Web Server (Http Server).

A web Server means: Handling HTTP requests (usually from browsers).

A Servlet Container (e.g. Tomcat) means: It can handle servlets & JSP.

An Application Server (e.g. GlassFish) means: It can manage Java EE applications (usually both servlet/JSP and EJBs).

You should use GlassFish for Java EE enterprise applications.