Struts
An open source MVC framework from Jakarta.
Spring
Spring is a layered Java/J2EE application framework, based on code published in Expert One-on-One J2EE Design and Development.
Expresso
Expresso is an open standards-based, enterprise-strength J2EE architectural framework for developing database-driven web applications based on open standards.
OpenCore
Midleware abstraction layer providing foundation for rapid development and smooth integration of open subsystems.