What’s lemmy? Is this lemmy. What’s piefed then, why are there multiple different communities for each topic ,

Lemmy and Piefed are two separately designed open-source Reddit software that anyone can spin up and host. The devs of both Lemmy and Piefed have their own instances, but there are many more.

People host their own Lemmy or Piefed servers and can federate with other servers to see the content on there.