Core war is an old game concept that dates back to 1984. If you imagine a simple CPU with small programs written in assembly language trying to wipe each other out, that’s Core War and you can read about it in a lot more detail on Wikipedia.
Inevitably for a game of that vintage there is a C implementation on GitHub by developer Emil Wallner. There’s an animated version of the screenshot showing the game play in action.
The programs (representing viruses) are small assembly language programs that move themselves around the virtual memory and duplicate themselves and try to wipe out the opposition. I’ll always meant to write one of these myself but for now there’s this.