Yet another derivation of the Raspberry Pi clip by PatrickT, this one is for any board with 4 holes arranged in a rectangle.
I used it for a 2-relay board here, but you can edit the parameters to fit your own board.
OpenScad source provided so you can edit. Change the params below:
width_base: width between the centers of the gnubs
length_base: height between the centers of the gnubs
board_width: width of the board.
Other parameters are also present to add screws for holes, and change all other sizes.