If you just need simple, then this is it. No gui, no automatic file manipulation, just double-click launching of factorio with the mod-set and config you want.
Basic usage is to create a folder that holds just the launcher and the mods you want to use (see full options block). Since the script likely needs an edit for each end user, it is presented a source. Open in Script Editor, edit the one line, and export as an Application. The script just dynamically creates a command line instructions with the '-c' and '--mod-directory' arguments based on its optional neighbors.
The script does not handle save games. Those still get stored off to the Application Support folder. You could, however, edit the config.ini file to point to wherever you would like top store your saved games, and use that in the launcher folder.