If yo will be using 3d to creatively impact your android UI, DAZ3d is offering free downloads of their pro versions of Bryce,Hexagon, and DazStudio until the end of February. The Daz link can be found in this article at the  bottom of the article. While Painter has an opensource clone called MyPaint which is quite good as a replacement, Bryce and Daz Studio do not have good opensource replacements. Its over $800 in free software.