If you mean notifications via MQTT on Android I use MyMQTT. For iOS there's and app called MQTT Tester that I haven't tried. If you mean notification directly from the puck via BLE there's nRF Connect for Android that works. For iOS it's called nRF Toolbox but I haven't tried it. My iPad is too old. For OSX I have no idea.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
If you mean notifications via MQTT on Android I use MyMQTT. For iOS there's and app called MQTT Tester that I haven't tried. If you mean notification directly from the puck via BLE there's nRF Connect for Android that works. For iOS it's called nRF Toolbox but I haven't tried it. My iPad is too old. For OSX I have no idea.