GameBase.exe is the main GameBase frontend application. If you run it with no command line parameters, and you have more than one GameBase database installed, then a selector window will popup, prompting you to select a database to load.
You can run GameBase.exe with your chosen database, in effect skipping the database selector window, by running it with your database name (folder name / .mdb file name) as a command line parameter:
GameBase.exe "My GameBase"