ROM switcher.
Looks like you've got KS 1.3 and 2.04 in there.
From the looks of it, you switch the ROM's by pressing CTL Left Amiga-Right Amiga for something like 5 to 10 seconds and it'll flip to the other ROM.
I see some jumpers at the other side so I assume you can switch the ROMs via jumper too. Standard solution was to install a switch via a wire there to switch the ROMs.
