Since Eucli-ea is being updated again, _CubeSnap standalone will not be updated. For future updates, go to Eucli-ea page and get it there: https://videogamemods.com/nomanssky/mods/eucli-ea-more-buildable-decorations-atlas-rises-edition/
A part of Eucli-ea, _CubeSnap is released as a standalone for AR as custom scene-updating is way too time-consuming to be viable for one person as for now for a mod with the scale of Eucli-ea, while _CubeSnap only consists of a few vanilla scenes and one or two custom ones and is therefore much easier to update.
It enables the infrastructure floor tiles and cube to be snappable onto cuboid rooms.
Since 1.4.2 of Eucli-ea snapping in _CubeSnap has been modified for the users to decided whether a doorway in the cuboid rooms or not:
To achieve this, first snap the object to the cuboid room, then look at the TOP of the cube room and rotate the object. On the other hand, to create a hole, snap the object, then look at the BOTTOM of the cuboid room and rotate the object