A simple circular coaster with a rim. I printed several with no top layers so as to expose the infill.

Dimensions:
110 mm diameter
5 mm height

Photos:
15% Hilbert Curve Infill
15% Archimedean Chords Infill
20% Octagram Spiral Infill

Using Slic3r or other equivalent software to create the G-code.

For a simple coaster, just print. For a more artistic touch print with no top layers and expose the infill.