Many of my friends use Twitter and we regularly comment on and retweet each other's tweets. I've recently been added to a Mastodon group which feels much more tight-knit. I've been playing dota 2 for the past few years and I regularly play with the same group of people. I also have a few discords I've been added to. I tend to lurk on bigger websites like Twitter, Reddit, HN.
Last.fm and Sonemic community are interesting in that they're entirely music based. The discussion revolves entirely around rating and categorizing music which is lovely if you think about it.
