Piefed is both an instance (piefed.social) and back-end server software that allows anyone to run their own instance (list of various Piefed instances). It works on the same ActivityPub protocol as Lemmy and Kbin/Mbin so they all interoperate with each other.

One of the cool things I like about Piefed is it seems to join the comments of various instances in cross-posts. On Lemmy, you can see its crossposted, but you have to manually check them out to see any comments on others. One cool feature I like over Lemmy. There's a few others, but I'd encourage you to check it out. You don't have to commit if you don't like it.