brid.gy automatically polls whatever silo you’ve connected to your site, looking for likes, responses, reposts, and so forth. It will then relay that information back to your site through... See Webmentions.
As an example, the author went to the Mastodon post POSSE’d from What Is indie-org.sh? and favorited it. After the next poll, a Webmention arrived representing that like and is now displayed here.