Pewmulator
Since CircuitPython is mostly compatible with Python 3, the only thing I really need to run PewPew games on a desktop computer is the pew.py library for handling the display and key presses. Turns out that PyGame is pretty much perfect for this — the code is even shorter than for original PewPew.
I have the emulator working now, available at https://github.com/pewpew-game/pewmulator and I have tested it with the two demo games for PewPew: tetris and snake: https://github.com/deshipu/pewpew/tree/master/games.
Now I can start thinking about the game itself.