Pre-alpha
Early builds go to invited testers. Enter the email address your invitation went to and the code that came with it, and you get the command that installs the game.
The command downloads the game and the map you choose, then starts it. Playing again fetches whatever changed since, then starts the game. If the first download fails, check the address and the code: they have to match the invitation exactly.
Linux and macOS
Run it in a terminal. To play again, run sh deadbelt.sh in the game's folder.
The game goes to ~/Deadbelt on Linux and to ~/Library/Application Support/Deadbelt/Game on a Mac (Apple Silicon only). To remove it again, run sh deadbelt.sh --uninstall; it asks before it deletes your saves.
Windows
Press Win+R, paste it and press Enter (a terminal works too). To play again, start Deadbelt from the Start menu.
Windows 10 or 11, 64-bit. The game goes to %LOCALAPPDATA%\Deadbelt\Game, your saves and settings to %APPDATA%\Deadbelt. To remove it again, run "%LOCALAPPDATA%\Deadbelt\Game\deadbelt-setup.exe" --uninstall the same way; it asks before it deletes your saves.
Nothing you type here leaves this page. Your browser turns the address and the code into a key, and only the key is in the download's address.