ZX81 Fly Low Hit Hard

download the .p file

Install a zx81 emulator such as EightyOne https://sourceforge.net/projects/eightyone-sinclair-emulator/

Set the memory size to 16k

Open the .p file in the emulator and play

The keys are x up,  n down. space bar or key to fire (also Cheetah joystick enabled if you play on real zx81). To play on real zx81 you'll need to convert the.p file to a wav file using the zxp2wav utility, then play the audio wave file over to the zx81. You'll need a 16K ram pack for that.