No instance, that’s the best part! I’m using Bridgy Fed which lets me federate select posts by adding a link to fed.brid.gy and sending a webmention. Check out the notes page on my site for the original posts. It even backfeeds responses via webmention.

I’m not sure Bridgy Fed supports regular at-mentions yet, but it should support replies like this, notes, articles, likes, and reposts.