Rails or Grails? [closed]

One other thing worth mentioning: the design philosophy of both framework is somewhat different when it comes to the model. Grails is more "domain-oriented" while Rails is more "database-oriented".
In Rails, you essentially start by defining your tables (with field names and their specifics). Then ActiveRecord will map them to Ruby classes or models.
In Grails, it's the reverse: you start by defining your models (Groovy classes) and when you hit run, GORM (Grails ActiveRecord equivalent) will create the related database and tables (or update them). Which may also be why you don't have the concept of 'migrations' in Grails (although I think it will come in some future release).
I don't know if one is better than the other. I guess it depends on your context.

This being said, I'm still myself wondering which one to choose. As Tom was saying, if you're dependent on Java you can still go for JRuby - so Java reuse shouldn't be your sole criterion.

I guess if you are a Java developer and want to have access to all the existing enterprise Java libraries and functionality... go with Grails.

Rails is more mature, has more plugins, has a bigger userbase, has better documentation and support available. It can also run on JRuby giving access to Java libraries if you require.

Grails has some interesting qualities, but can't claim to be up there with rails just yet. However, if you're predominantly a Java or groovy developer you may prefer it. Otherwise though, I'd suggest using Rails for medium sized projects right now.