A thin extension to pygame.sprite.RenderUpdates to allow user-defined layering of sprites.
I got tired of trying to control my sprites' relative layers with an OrderedUpdates, so I wrote this alternative. It works just like Ordered- or Render- Updates, but each sprite must have a "layer" attribute. That's an integer describing its position relative to other sprites. Lowest is drawn first. Where two sprites have the same layer, the one whose bottom is highest is drawn first.