This Thing is a fully customizable ventilation grill that allows you to construct a wide range of ventilation outlets just by changing some parameters.
Use openscad to configure it.
The author remixed this model.
Since the real world is not perfect, i've added a configurable edge.
This hides imperfections if you try to use this as a cover for a ventilation vent. Pipes often stick out and ceilings around a pipe are not completely flat. The edge helps hiding this.
Its configurable and can be disabled to get the normal behaviour.