Like the title says, these are parametric stacked Multiboard tiles. You can use the parameters to define the tile dimensions as well as the number of core, side, and corner tiles to print with those dimensions. There are STLs here for a number of “starter” 3×3 tile grids of several different-sized tiles: 3×3, 4×4, 5×5, 6×6, 7×7, and 8×8. You can use the Customizer or the SCAD file to generate stacks of arbitrary files.

In general, if you plan to make an M×N tile grid, you need (M−1)×(N−1) core tiles, (M−1)+(N−1) side tiles, and one corner tile. (This assumes you don't want tile teeth sticking out the side and top of the finished board. If you're okay with that, just print M×N core tiles.)

If your tiles are not square, you will have to print one set of side tiles separately, because this model always puts the teeth on the X side of a tile, but a full grid needs one side to have the teeth on the Y side. If you're printing an M×N grid (where M is the width and N is the height) of X×Y tiles, print M−1 of the X×Y side tiles in the stack with the core and corner tiles listed above, plus a separate stack of N−1 of the Y×X side tiles.

You have to enable ironing in your slicer to make sure the layers are reasonably separable.

The source repository for the OpenSCAD base is https://github.com/asciipip/multiboard-parametric-stacked .

Note that the CC license listed here is not correct. These are actually under the Multiboard License. Its overall characteristics are similar to CC BY-NC-SA, but its specifics are a bit different.