WhatsPromo can help you in your announcements within an organisation or for advertising purpose, using your AccessibilityService API.

◼ broadcasts a message to a list of people.
◼ straight forward and hassle free.
◼ makes use of AccessibilityService API
◼ Free to use.
◼ No registration required.
◼ Your personal data is safe and not required to use the app.

which It uses native platform so that the broadcast becomes straight forward and hassle free.