Let your user talk to each others? which tool?

Hi fellow indie hackers!

I have a quick question. I built a side project which I kept simple by only using emails and a small landing page.

Now without overloading my members emails I would like to let them share with each other. I am thinking something like FB groups but I don't want to use FB :)

I want to keep it as low as possible in term of maintenance (side project ;) ) but I really need to engage people.

Thanks for your ideas