Any idea what this part is?

[livingonwheels]

It was in the bottom of a complete in box Commodore 64, but I don't think it has any relation to it:

[Albert]

Looks like a hardware copy protection dongle that software can check to see is present before running.  Could be for any system that uses DB9 ports, I've see dongles like this on the Atari ST and PC before.  Could certainly be something else, though.

 

 ..Al

[+OLD CS1]

Yup.  Definitely some kind of copy protection dongle, but you will be hard pressed to figure out what system and software it is for with the ubiquitous DE-9 connector.  Other than RS-232/C, those 9-pin ports are mostly software definable.  For instance, on the Commodore 64, the CIA ports which drive the joystick connections can have each pin, five presented at the connection, set for input or output.  That combined with the two potentiometer pins, +5V and GND, provide a incredible number of potential combinations.

 

EDIT: SAFE to assume it is for the C64, though, considering where it was found.  So, you might be able to narrow it down to the software included with your haul.

[livingonwheels]

2 Cartridge games were also in the Commodore's original box. Mutant Camels (no label) and Music Machine 64. A bunch of floppies were included. One box of floppies labeled "Master Discs" (which I have another topic concerning). Also random booklets and paperwork, cib floppy disc drive, C64 modem. Seems to be an older unit (no S-Video port). Pictures below.

 

[ktelep]

I have a similar Dongle, mine is blue.   Looking at the titles on the disks, I believe that the key you have is for KMMM Pascal.

 

Looking at page 5 of the doc (Page 7 of this PDF: https://www.lyonlabs.org/commodore/onrequest/KMMM_Pascal_Level_IV_Compiler_Translator_Reference_Manual.pdf) they talk about having to put the security key in to the joystick port in order to compile and edit applications.

 

Mine is blue and serialized, and it's not Paperclip (I already have one of those)