One of the more unusual social media platforms, and one which I did not anticipate to be as inviting and as interesting as I have ended up finding it to be is Disqus. What began as a kind of plug-in feature to be added to blogs and pages as a way of managing comments has morphed seamlessly into a kind of forum unto itself. There are many smaller blogs which use this forum, but also some large ones (e.g. The Atlantic and Rolling Stone).
From a personal interest point of view one can involve oneself in a ton of interesting conversations very quickly and from a professional standpoint, one can bolster one’s SEO standing in terms of your name, or subject, or associating your subject with your name. It is also a way to get one’s point of view seen and read, and comment threads can be almost impossibly lively. One also has a number of security and privacy settings to avoid things getting overly personal. Feel free to argue with me!!