Glassfish is an application server project by Sun Microsystems made for the Java Enterprise Edition (Java EE) platform. This free software has the name of Application Server 9.x of Sun Java System as its commercial version.

Based on a source code donated by Oracle Corporation’s TopLink persistence system and Sun, it used a derivative of Apache Tomcat as the servlet container for serving Web content. It has an added component called Gizzly which uses JAVA NIO for speed and scalability.