The kbdmux keyboard driver provides support for basic keyboard multiplexing. It is built around the idea of a "super keyboard". kbdmux acts as a master keyboard consuming input from all slave keyboards attached to it.
Slave keyboards can be attached to or detached from the kbdmux keyboard driver with the kbdcontrol(1) utility.
kbdcontrol(1), atkbd(4), pcvt(4), syscons(4), ukbd(4)