I'm enough of a keyboard fanatic that this is driving me nuts!
That key in the lower-left is either a Fn or SysRq, I bet.
The original IBM PCConvertible used a similar - but not quite matching - layout, and other laptop-makers copied it.
Now, I inherited an 8086 Sharp lunchbox with a compact, removable keyboard that clipped onto the front- sort of Compaqlike, but smaller (it had a really nice LCD that could tilt out/collapse flat, on one of those fake-pneumatic spring mechanisms)... It too was fond of SysRq for its setup TSR (loaded from ROM, if I remember right!), and may've had it in just such an odd position; it's been too long. Its latches were on the sides, but I think it had a bit of lip below the spacebar... maybe.
Problem is, I can't remember the model number, and I don't have it around to go look at!
Of course, it could also be some generic compact aftermarket 'board, but those usually put the arrow keys in the same line as everything else- cheaper to manufacture that way.
The keys to the left and right of the spacebar are doubtless Alts, unless it really is from something odder than a PC.
