GlassFish is an open-source Jakarta EE platform application server project started by Sun Microsystems, then sponsored by Oracle Corporation, and now living at the Eclipse Foundation and supported by OmniFish, Fujitsu and Payara.

This allows developers to create enterprise applications that are portable and scalable, and that integrate with legacy technologies.

Built on a modular kernel powered by OSGi, GlassFish runs straight on top of the Apache Felix implementation.

GlassFish is based on source code released by Sun and Oracle Corporation's TopLink persistence system.

It uses a derivative of Apache Tomcat as the servlet container for serving web content, with an added component called Grizzly which uses Java non-blocking I/O (NIO) for scalability and speed.