GoToSocial★★★★☆A lightweight Fediverse server, with a clean web interface for viewing public posts. Compatible with Mastodon apps and interacts with other ActivityPub platforms.
Postmarks★★★★☆A self-hosted public bookmarks/linkblogging server (think Delicious or Pinboard) that can interact with Mastodon and the rest of the Fediverse.
RSS Parrot★★★★★A simple Fediverse service that follows an RSS/Atom feed and creates an account you can follow from Mastodon or any other ActivityPub site.
Snac★★★★☆Extremely bare-bones social networking server that runs on low-resource machines, works on the web without cookies or JavaScript, and still interacts through ActivityPub with Mastodon, GoToSocial and other Fediverse software.