I mean the kind of device that would connect to any random server's VGA, keyboard and mouse port, and make this server accessible via VNC even when it's in the BIOS menu or has no OS installed.
I found some on eBay and Aliexpress, but the descriptions are very terse, usually just some HP (or whatever brand) part number, and it is not clear whether they support VNC or require some proprietary tool to access.