Matthias Goerner's 3D print: http://shpws.me/SZbN
Countdown d24:    • From Sphericons to Countdown dice  
Matthias' version of the construction of the polyhedron: http://www.unhyperbolic.org/sydler.html
Demonstration of the Wallace–Bolyai–Gerwien theorem by Dima Smirnov and Zivvy Epstein: https://dmsm.github.io/scissorscongr...

Brooks and Matelski were the first to make an image of what we now call the Mandelbrot set. This image is in the public domain: https://en.wikipedia.org/wiki/Mandelb...

According to Wikipedia, Pingala studied the relations between the numbers in what we now call Pascal's triangle, but the first appearance of these numbers arranged in a triangle was due to the Persian mathematician AlKaraji (953–1029).