Karabinder rule to make option launch Spotlight, ala Windows.

spotlight.rule.json

{
    "description": "Option launches Spotlight",
    "manipulators": [
        {
            "from": {
                "key_code": "left_option",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "left_option" }],
            "to_if_alone": [
                {
                    "key_code": "spacebar",
                    "modifiers": ["left_command"]
                }
            ],
            "type": "basic"
        }
    ]
}