Grails is an open source web application framework that uses the Groovy programming language. It is intended to be a high-productivity framework by following the "coding by convention" paradigm, providing a stand-alone development environment and hiding much of the configuration detail from the developer.
In Grails 4.0 Micronaut will take over as the parent context for Grails applications and much of the internal wiring of Grails will be based on Micronaut instead of Spring