"Flatland Lock" from the book "Leonardo's Mirror & other Puzzles" some pages available in google books and depicted here ...
The object is to remove in succession the four linkages (red green orange blue) the grey blocks are not movable, and the dark blue are empty space. the solution in page 4 on the above document:
and in page 5 there is a printable shape so we can construct a real Flatland Lock from paper easily.
there should be a commercial plastic or metal version of this lock.
I'd read about Flatland before but not heard of this lock, thanks for sharing!