PieFed is a completely different codebase than Lemmy, but that is aiming for the same paradigm and uses compatible federation so they’re cross compatible.

So it’s basically another option for people running instances to pick running a PieFed instance over a Lemmy instance.

That having been said, I heard they built some features Lemmy doesn’t have that people like. Like I think I heard it groups the same link posted to multiple communities so you can see a more overall sense of the discussion? Or something? I haven’t used it…