Cavatappi is a tubular pasta with a cork-screw shape which is available with or without ridges. This (and other pasta) is frequently referred to as macaroni in many regions of Italy. The Italian word cavatappi means "cork screw". The ridged version holds on to sauces better than the smooth.
Use cavatappi in baked pasta dishes or even pasta salads. It is popular baked with tomatoes, eggplant and Italian sausage.
This is a less common pasta shape in the U.S. but can be found in Italian markets or some other well-stocked grocery stores. You can always buy it online at Amazon.com: Cavatappi where they have several good brands available including De Cecco, Colavita, and DeAllo.
If you don't have cavatappi, then you can substitute: