GIFs based on patterns generated by Eva Schindling's L-Garden program, a Java utility made with the Processing programming language. Anyone can load the applet and make one of these but it's primarily a drawing program, not an animation program. Here, the transparent one is made from Schindling's example GIF (hat tip Issac). The non-transparent one is a screen capture of a drawing in "grow" mode, as it appears in the applet.