I always wanted to see a plugin/widget for WordPress (and generic JS plugin for non-WP sites) that let you input the URLs for your friend's blogs, and it pinged

I always wanted to see a plugin/widget for WordPress (and generic JS plugin for non-WP sites) that let you input the URLs for your friend's blogs, and it pinged their site to tell their widget (if they had it) that you've added them to your blogroll, and let them add you back. A simple decentralized version of follow/friends for blogs and sites in general, without them needing to be on the same platform.