Smooth wavy pencil cup.

Designed in FreeCAD, the outside has a very organic smooth curvy shape.  There are two STL files.  The one with 'dense' in it's name is a very dense mesh for extremely smooth rendering when printing.   The standard STL will have slight faceting that's visible with reflections.   
I prefer the dense version for the amazing way that light reflects off of it with a shiny filament.  as your view shifts, the light moves in many different directions along the surface.