It's called an "ALTERNATOR DECOUPLER PULLEY TOOL SET"
• Includes all of the tools required for removal and installation of ADP (one-way and overriding/freewheeling)
• Includes five tools designed for North American vehicles
The reason for this tool and your special alternator is to allow it to decouple if there's reverse rotation imparted into the pulley drive.
It was too logical I believe to allow the belt to slip just a tad when you shut off the engine ... that was the practice up to that time.
I can see how marvelous this is and all ... "improve the breed" 'n all ..... but just maybe this is a CEO's brother-in-law with a matchbook degree in Automotive Engineering who needed a job with a desk and an office and his name on the door ... with some hot 'n cold-running secretaries.
I dunnow how this happened and it might just be some serious overengineering for a problem that really doesn't exist ......... but there's gotta be at least a semi valid reason for it.