I want a software for chatting with some group(s) only that is similar to the WhatsApp in all other aspects with the following requirements
1) Should not be based on mobile number so that only few people can be involved (secret or closed app)
2) Each group is asked a time and it will give some kind of (audio) reminder or notification for regular intervals of such timings.
3) No need of Google backup like Whatsapp do.
In example to the all points. consider the following situation.
You need to send some assignment document once in two days for group-1 that contain five people, results video once in a week for a group-2 that contains ten people, question image once in five hours for a group-4 of six people and an instruction text once in a year to two students only.
In WhatsApp I can open open four groups and keep students. But the reminder thing is unavailable. It also needs my Google account to backup info and anyone with my mobile number can see me.