what is the relationship between RenPy and Pygame?
Ren'Py is a game engine that people use to make specific types of generally narrative-heavy games. Visual Novels, Life Simulations, and simple RPGs are all within what Ren'Py was intended to help make.
For ten years, Ren'Py was based on Pygame, to the point where the Pygame API is included in various places in the Ren'Py API. About a year ago, it became clear that SDL2 would be necessary for Ren'Py to keep supporting Android and add iOS support, so we wrote Pygame_sdl2, a reimplementation of the Pygame API over SDL2. (Pygame_sdl2 isn't complete, as it needs help from people who understand buffers and the pygame test suite.)
Ren'Py has a number of tools that are used to package games for mobile platforms - RAPT is used for Android, while Renios is used for iOS. These tools are generally written in a way that they can be used to package arbitrary games written using pygame_sdl2.
Ren'Py itself also comes with a launcher that can one-click package a Ren'Py game for Windows, Mac OS X, and Linux - with a few more clicks, it also takes care of Android and iOS packaging. This isn't designed to work with arbitrary pygame code, but could plausibly be changed to do so.
Due to terrible social skills, I haven't really contributed much of this Ren'Py work back to pygame - and the one project I did contribute, pygs4a, turned out to be a technological dead end. I'm trying to change this, if people are interested.