The IndieWeb is using the idea of Webmention to allow site-to-site communication and commenting. This allows interesting things like Threaded conversations between WordPress and Twitter. Here’s a good recent example with the copy on my website and a separate copy on Twitter.
And finally there’s an interesting wiki experiment that Kicks Condor and friends are doing that is worth checking out if you didn’t dig deep enough into @AGWilsonn’s links to see it. (See the comments on that link for more details.)