You need to have SDL2 installed. I probably should have made that clearer in the install instructions. If you're running Windows, it should be enough to put SDL2.dll in the same directory as sbcl.exe or somewhere in your PATH.
Viewing post in BULLETWAR!! jam comments
I made a Windows binary:
https://drive.google.com/uc?id=1I7-_EGWJzWIZPbXM9lgS2tKjxSd87efP
It doesn't have sound, but it should actually work.
https://drive.google.com/file/d/1xDogNJAYhnPa_J_tZ9NTHyXEQvz-B7tR/view?usp=shari...
Here you go. I should probably have spent more time on this stuff instead of broken multiplayer...