[herbcso]

Mosquitto seems to be the de-facto "standard" choice for a Pi. Easy to set up and definitely lightweight.

[Abishek_Muthian]

Yes, Mosquitto from default repo works as it should without any trouble.

As for android client, I recommend this[1] but it requires Tasker Autonotification plugin to display notifications.

[1]https://play.google.com/store/apps/details?id=in.dc297.mqttc...