Close all apps except the frontmost visible one. macOS only.

close-other-apps

#!/bin/bash

# get frontmost app
frontmost_app=$(osascript -e '
    tell application "System Events"
        POSIX path of (file of application processes whose frontmost is true and visible is true)
    end tell
')
escaped_frontmost_app=${frontmost_app//\//\\/}

# write automator workflow to temporary file
tmpfile=$(mktemp)
plutil -convert xml1 -o "$tmpfile" - <<END
{
    "actions": [{
        "action": {
            "ActionParameters": {
                "appException": false,
                "fileNames": ["$escaped_frontmost_app"],
                "saveChanges": true
            },
            "ActionBundlePath":"\/System\/Library\/Automator\/Quit All Applications.action"
        }
    }]
}
END

# run automator
automator "$tmpfile"

# cleanup
rm "$tmpfile"

If you know a more elegant way, I'm curious! I tried to access the parameters directly in Automator; without luck.