How to setup a wireless network without internet for people within an apartment building?

Hi, is it possible to setup a wireless network WITHOUT internet for people to communicate with smartphones connected to the network via a basic router?

There isn't many people with internet in my building and with social distancing requirements it is difficult for them. Some of them don't even have phone service. Can I take basic router and set it up so folks can talk or message each other with certain smartphone apps? I would not be able to leave a computer connected to it but I have a computer to use to set it up.

And what kind of router would be necessary?

I have tried a basic internet search

Thanks!