I dont know what it is but can have some guesses,
The cut in the corner is so that a object with a corner can be put into it or the tool used on an object with a corner,
As i say i dont know but a wild guess is somthing for forming mouldings on a plastered wall or such like,
It could be a gague for some sort of mouldin on wood work as well,
I dont think it is a lockpick as such but could be wrong,
Its interesting to say the least,