Snap To Floor is a Blender port of a C4D plugin, originally brought to Blender 2.8 by Pixel Egg Studio. It keeps your object snapped to the floor while you move or rotate it, so the model stays down to the floor as you work. Snapping also applies while animating.
The add-on provides realtime feedback and supports rolling away, along with snapping during animation. A later update added the ability to snap to the 3D cursor's z position and an option to apply snapping to all meshes in the scene. The developer's plan lists working for groups of objects and snapping to any 2D plane.
Snap To Floor is distributed under the GPL license and lists Blender version support ranging from 2.8 through 4.3. Support and discussion are available via the developer's Discord, Twitter, and a Blender Artists thread. Documentation is included with the product.