So the Ruby on Rails people asked the group that started the "Groovy on Rails" effort to stop using the term "on Rails" (whatever). That is why they have the name Grails now. They didn't ask me and I have to say that this week of building a first end to end app for production use with Grails was quite groovy.
First, I do like the coding by convention approach that allows less code and less configuration to be used. I also like that what configuration is there is in the form of classes not XML. We made an app for the ANDRILL effort and it should see the light of day soon (ie be reviewed and deployed).
During the course of this development I was very impressed with how the various packages in Grails: Hibernate, Quartz, AJAX (via prototype in my case), Spring (obviously) and the GORM objection relation mapping all work. I am very keen to make up a Quartz job and then use the jabber resource to make a job that looks for changes or additions to the database and then IM's me. That is more for me, the real version would likely report via email.
We did run into some issues (Grails is only version .3 after all). An issue with binary uploads in a none scaffolded controller (I assume the generated static code is somehow out of sync with the dynamic scaffold generated code). Also had an issue with using the remotelink tag for AJAX calls vs using the remoteform tag for the same effect. We resolved this by just not using them :) but I need to report this to the Grails people to see if it is a known issue or something I was doing wrong. Getting used to the scope of certain classes and methods took some getting used to as well, but that is more just my ignorance with how the plumbing was working at the start of this effot.
Having full access to the all the wonderful Java classes makes Grails a no brain-er for me over Ruby on Rails. I have to admit I am a bit sad that Sun seems to be in love with Ruby (via jRuby which ironically is also a codehaus effort at http://jruby.codehaus.org) and pays little if any attention to Grails so far (hopefully this will change). Yes, though jRuby the Ruby syntax gets access to the classes as well. We will see how this all works out. I was interested to find that one of the key people in the Apache Geronimo effort is also one of the key Groovy people as well. Ruby has some very cool aspects to it, but I think the JVM is a better host for it than as a stand alone app directly on top of the OS.
In a final experiment (ref: InfoQ Grails + EJB and a Graeme Rocher blog entry) we used entity classes (not entity beans) that we generated via Netbeans for a database and dropped the POJO's into a grails app and were able to get read and write access to the db via the grails app using these entity classes as our domains with simple generated controllers and views. We had some issues with primary key mappings, but nothing too hard for us to work around. This was interesting to me since I could use the entity classes along with Hibernate to do the data access work and then Grails as an lightweight flexible dev layer on top of that. Grails lacks sophisticated buses like Service mix and others, but I am not certain I need or want those at this time (or that I can't do what I really want inside the Grails framework anyway).