This week's book giveaway is in the Programmer Certification forum. We're giving away four copies of OCP Oracle Certified Professional Java SE 11 Programmer I Study Guide: Exam 1Z0-815 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
Struts 2 is a request based MVC web application framework. In multi-tiered applications its used as the presentation layer. Seam on the other hand is an application framework that can be used to build fully fledged enterprise applications (think spring). It enhances JSF a lot (JSF is another web framework, but it's component based rather than request based), and integrates it with EJB (if you want to use it) SEAMlessly (hence the name). It has a lot of features. If you want to learn more about it, look here for an overview, or get Seam in Action for the details