I found a couple of these at the surplus place a while back, but I bought four and only need one, so...
This is a low voltage on-off-on key switch. It's normally open, and the key can only be removed in the "off" position, but there are two different on positions and two different keys. The round key can go either left or right; the square key can only go right. That bit of trickery may or may not be useful - if it's not, just wire the left and right connections together and use both keys...
edit: SOLD!