Struts 2

After the release of WebWork 2.2.2, the WebWork and Struts communities began a merge that will eventually produce Struts 2. This merger combines these two "action based" frameworks  as it is told .

• Struts 1 and Webworks (WW 1.X, 2.X)  comparison feature for feature
• Interview of Jason Lightbody from the  Webworks team  about Merger
• struts2 wiki   and WW wiki
• XWork : "

  XWork is an command-pattern framework that is used to power WebWorks as well as other applications.
  XWork provides an Inversion of Control container, a powerful expression language, data type conversion,
  validation, and pluggable configuration"

• struts1 vs struts2
• presentation part I ,  presentation part II
• migrating
• Struts Planet 
• download
• example

Compared to SpringMVC,
you sacrifice some cleanliness but there is a lot more work done in
certain areas, for example client-side validation, a strong Interceptor
framework and a nice graphical flow
designer – this latter is also a strong area, with WebWork being one of
the pioneer adopters of the freshly unbundled RIFE Continuations package.