If you have several projects on your machine, you can switch between them by going to the Project tab and double-clicking on the project you want to visit.
You might notice that the projects which have some unprocessed incoming scripts have a little wave added to their icon and the ones with files checked out have a yellow icon.
If you select Visit item from the Project menu, you'll be simply transferred to the Projects tab.
You will notice that the Files tab has a Details screen at the bottom which lists curently active projects. Double-clicking a project from here will open that project.