That could be a pretty useful thing for adding new actions that are applicable to projects. (Maybe an action that interacts with Roman's Project Packager, for example.)
So, this is how I added the action (click to enlarge):
But, the best part is that I discovered how to do this by just hanging out in the System Filesystem Browser which you get when you create a module project. It lists all the layers made available by all the available modules. So, that's how I found out about the existence of the ProjectsTabActions folder... And then I just used the Action wizard to create the action and tweaked the layer.xml file so that the action was registered in the ProjectsTabActions folder instead of somewhere else.
So, whenever you create a module project, you get the System Filesystem Browser, which is an extremely educational tool, allowing you to discover folders that you never knew existed. Here, for the uninitiated, is part of my System Filesystem Browser (click to enlarge):
What's also cool about the System Filesystem Browser is that you can drag and drop items within the folder, which results in tags being added to the layer.xml file for sorting the item within the folder. In fact, I didn't type anything in the layer.xml file shown in the second screenshot above (apart from the name of the ProjectsTabActions folder). It was all done for me by the IDE. Something else that's cool is that everything that the current module is going to add to the module universe is printed in bold in the System Filesystem Browser. Really handy. Go ahead—enlarge the screenshot above and notice the bold folders and then enlarge the second screenshot above and notice that the bold folders are the ones that are in my module's layer.xml file. Handy, right?