My social network for two is called text messaging. Lots of prior art here, I think. Others might use Signal, Slack or even MS Teams. Heck, email works.
@frankm I think you are on the mark - lots of options already exist. I thought of my own tool as well (http://fedwiki.andysylvester.com:443/) and Colin Walker's version (https://mst.andysylvester.com/).