A mate of mine found 4 of these in a building (a house I think) he was renovation - anyone have any idea what it is or what it is used for?

It is made of plastic, and the slide mechanism in the centre has 3 positions:
Position 1 - everthing is fully retracted.
Position 2 - the 2 small blades at the positions marked 'Caution Blade Opening' are extended.
Position 3 - the 2 small blades and the pointy thing at the corner marked 'Caution Nail Point Opening' are all extended.

This thing is made of plastic, and is marked 'made in china' (big surprise).

Got three myself! Corner shelves in a room, the blades go into the wall and hold the shelf into place

So are they just sort of temporary?

You lie, sounds more like terrorist hijacker frizbys.

They are very temporary if you put anything heavier than a Kmart catalog on them.

Jeff,

As Joel said, they are secret Ninja weapons, be very careful.

They are definately permanent - Life is temporary.

Regards,

Matt.