Vic-Switch Multi User System by Handic

Info from the 64-wiki:
 
The VIC-Switch was manufactured in Sweden by Handic Software AB for Commodore and allows up to 8 VC-20 and C64/128 (not in Burst-Mode) computers to connect to a single shared device like disk drive or printer on the serial bus. Apparently there is also a version for connecting up to 16 computers.