A complex modification rule for Karabiner-Elements, this will change caps_lock to left_control if pressed with other keys, and change caps_lock to escape if pressed alone.

Karabiner-Elements__capslock2ctrl.json

{
    "description": "Change caps_lock to left_control if pressed with other keys, change caps_lock to escape if pressed alone.",
    "manipulators": [
        {
            "from": {
                "key_code": "caps_lock",
                "modifiers": {
                    "optional": [
                        "any"
                    ]
                }
            },
            "to": [
                {
                    "key_code": "left_control"
                }
            ],
            "to_if_alone": [
                {
                    "key_code": "escape"
                }
            ],
            "type": "basic"
        }
    ]
}