More than 90 people want to send them a group message. What software do you use?

Yes, you can apply to the telecommunications bureau. I'm from Guangdong, and our company applied to the local telecommunications bureau for mass short message service. Very cheap, tens of dollars a month, very affordable.

It is to install something similar to MONED on the mobile phone, then install the software, make some settings, and send messages in groups.

I don't know if your telecommunications bureau has this service, it should have both. If not, you can find some internet companies. They should also have such amateurs, but they are more expensive.

If you just want to install software on your computer, you can send it in groups. If you don't need money, it's impossible. Even if you have such software, you should register it. Registration costs money.