This sounds like an odd beast because it is. It might even be completely unwarranted. So what problem is it trying to solve? Let’s say you have a project and in that project is a maven plugin. Because you’re a kind soul, you also want to offer a gradle plugin but you don’t really want to deal with two different builds. Enter the graven maven plugin.
In an ideal world, gradle resources would be in a repo somewhere fetchable and you could just add your dependencies to your pom.xml and move on with life. If they exist somewhere I haven’t found them. What this plugin does for you is bridge the lifecycles of maven’s build to gradle so that you can trigger a gradle build of your plugin from the comforts of your maven build.
This plugin will also help synchronize dependency versions defined in your maven build with those needed by gradle to build your plugin. And once all that’s done, your gradle plugin artifact will be attached to your maven build as if nothing sneaky happened. With a bit of luck, you’ll hardly know you’re running gradle at all!