On Land

Environment Information
At Rill Architects we run ArchiCAD on Mac OS X. If you work at Rill, this is your stuff. If you don't, but you work in ArchiCAD, you may find something interesting. Anybody else, I don't know.
RSS

Update. The AC11 versions have RCP-awareness.

Location: 13 Special Construction

Two objects (primarily) for cutting coved recesses into ceilings, using solid element operations. One's a circle, one's a rectangle. Guess which is which. The parameters of each are similar.

The fillet radius must be less than or equal to the height. The resolution of the fillet is controlled by the Fillet Facets parameter. For the disc, the Resol parameter controls the resolution of the circle.

You can turn the objects upside-down with Flip Z. I can't imagine many cases for doing so, but you never know.

In practice, your ceiling slab will be the target, and the object will be the operator.