Special Interest Groups and Communities of Interest.
Especially with long form text and commentary.
What's the best platform for these in 2018? IRC, Usenet, Skype Groups, Yahoogroups, Mailing lists have all died. Most phpBB/vBulletin sites have died. G+Communities and GoogleGroups are f*cking useless. Reddit works but the geeky barrier to entry in the UX is too much. IMHO, right now Facebook is the best with the most engagement. Though it too has problems.
Follow friends and discover new ones. Publish anything you want: links, pictures, text, video. This server is run by the main developers of the Mastodon project. Everyone is welcome as long as you follow our code of conduct!