What are /r/mathgifs' favorite Products & Services?

From 3.5 billion Reddit comments

Have you looked into GeoGebra? It's perfect for that kind of Euclidean geometry play. The GIF exporting feature is a bit annoying to work with, but if you're just looking to understand things yourself then you don't want GIFs, you want interactivity!

GeoGebra offers a whole lot of features that deal with the postulates, and you can drag objects around and have the relations update automatically. It's really awesome. Give it a try!

https://www.desmos.com/calculator/a8ew8sevn7

The shadows are really simple, later I made better shadows by defining two edge points and I draw a line based on the angle between the light point and the edge points.