I was sailing thru the net to see if there is anyone doing Rails framework on Java?. so some of the following guys who are doing few things similar to rails, not all.
# Trails: domain driven development framework in the spirit of Ruby on Rails or Naked Objects. Uses Spring, Tapestry, and Hibernate. Probably this one has a long way to go. Not too much happening in this area.
# Sails: Purely framework designed by keeping Rails in mind. Have a download section.It would be interesting to download and play with it.
# Grails: Sounds the closest one to rails, including controller/model generation, scaffolding etc, its written in Groovy
# JBoss Seam: Probably most active and adopted project as compared to above. Seam uses EJB3 and Hibernate (both, I wonder why?. Probably things around Transaction support and things like heavy weight vs light weight components usage).
I will keep watching this space and add if i run into any other puppy who wants to be or do things like rails in Java.