For MacBook users wondering why the download doesn't work, it is because the file provided is literally called OVERD0SE-1.0-PC.zip. That's a PC/Windows file, NOT a Mac file. Which is why Mac users can't play the game because it isn't the proper file for Mac.
When I download other visual novels, the Mac version is usually labelled something like "_____-1.0-mac.zip".
I'm not sure why this hasn't been fixed yet considering a few comments have already pointed it out. Hopefully the creator uploads a proper Mac version, as I also want to play the visual novel but can't.