Those images were made with a program that was written to do mathematical computation of the surfaces of various functions.

If you want to find some nice brushes that can be used in a variety of media for free here is a link to one resource that i downloaded some brushes from.

http://www.photoshopsupport.com

browse around there is always new stuff on this site along with more add-ins than just brushes.

Check the right panel for what you are looking for.