How about an app to make countersunk holes? I think it would be very useful. For example, you select the hole diameter, diameter of the countersink, and depth of the countersink. The app would generate a graduated set of concentric circles, like shown in the picture below:
credit for image goes to sketch42
Most of the more serious CAD packages can do this programatically. Fusion360, OnShape and SolidWorks certainly do (I imagine Rhino does too). Here is the hole generator in OnShape set to countersink mode as an example. The CAM part of however you send your designs to be converted to G-code would do the tool path conversion of the hole. The fancier hole generators worry about whether the hole is tapped or drilled, clearances, head-shape, etc.
