Error Opening the Application "Steam.app"

If you encounter the error "Cannot open application 'Steam.app'" when trying to launch the downloaded Steam on macOS 10.11 El Capitan, follow these steps. Note that the correctness of this method is not guaranteed...

1. Right-click on the Steam icon and select "Show Package Contents"
2. Navigate to Contents/MacOS
3. Locate steam.sh, then open Terminal and drag steam.sh into it. The full command should be:

$ /Applications/Steam.app/Contents/MacOS/steam.sh

It should look like this. Press Enter to execute.

4. Steam and Steam.app will be updated, and steam.sh will disappear.
5. Attempt to launch Steam.app again by double-clicking it. You will get a message saying it cannot be opened because it is damaged.
6. Use Terminal again. Drag Steam.app into Terminal to input the path, then move the cursor to the beginning of the command and enter xattr -rc.

The full command should be:

$ xattr -rc /Applications/Steam.app

It should look like this. Execute it.

7. Double-click Steam.app once more. It should now launch successfully.