A new .rpl file is created in the current active project folder. The name of the project list file is Projects.rpl. (If a file with this name exists in the folder, a number is added to the end of the file name, for example Project1.rpl.)
The current active project is saved as an attribute of the project list, so when you reopen a project list, the active project is the project that was active when the project list was last saved.