I got impression and started building small application based on this framework. Grails is based on groovy dynamic languages. Groovy, you can say a superset of JAVA language. It runs under same JVM what you use for JAVA. So JAVA and groovy programs can run together. Here i am giving couple of link for tutorial. Grails framework is supported by springSource, creator of Spring framework and it supports well. It also supports all modern Object relational Mapping tool like hibernate. A based way to learn to watch screen-cast videos available in grails website and try along with that.
1. grails website
2. groovy website
3. git installation
4. screen-cast tutorial