Documentation for GMaven has moved.
GMavenPlus attempts to fill much of the role GMaven did now that GMaven is discontinued.
An alternative approach to Groovy and Maven integration is to use the groovy-eclipse-compiler plugin for Maven. There are benefits and disadvantages to each approach. For more information on this as well as a description of the differences between gmaven and groovy-eclipse-compiler, see Groovy-Eclipse compiler plugin for Maven.