This is a simple recursive snowflake in BlocksCAD. You can customize the parameters by going to the project page and choosing "Create my own".
The basic shape is done by drawing a line, and then doing recursion for six scaled-down and rotated/translated shapes. The result is one sixth of the 2D image, which is then extruded and rotated six times in a loop, as per Challenge directions.
To print, choose one of the ones with thicker interior walls. I used a razor to help remove the delicate snowflake from the bed. It had some threads which actually helped keep it together. Transparent white PLA made it look very much like a snowflake.
The Customizer here is made by exporting the BlocksCAD file to OpenSCAD, and then moving the variables to the top of the file.
December 22, 2017: Added an adjusted version where the inner segments are thicker, which makes the snowflake more durable when printed.