POSSUM is Pete's Own Space Shooter Using Microcontrollers!
It's a plain old vertical space shooter, written for the 32Blit and PicoSystem consoles, but also working under SDL on a variety of desktop platforms.
The code is all released under the MIT License, as usual. The graphics are from Gustavo Vituri on itch.io, and in accordance with that license, they are not included in this repository.
They are free, however, so you can grab them directly from itch.io (stopping to give the talented Mr Vituri a donation) and drop them into the assets folder if you want to build from source.