In case anyone else is wondering, but doesn't feel like searching the web:

Piefed is similar to Lemmy. It federates with the Lemmyverse, Threadiverse and Fediverse. But with some additional features and differences:

• User flair. (Does not federates to Lemmy)
• Hierarchical subjects/magazines. For example, there might be a subject like art with sub-subjects like art/paintings and art/statues. (Should be possible to follow these from Lemmy)
• Instance blocking doesn't just block communities but also comments from said instance.
• ~~Only supported by Interstellar right now, as far as apps go, but Voyager is also planning to add support.~~ Supported by apps like Interstellar, Summit, Voyager and Boost. Photon also plans support.
• Written in Python instead of Rust, but somehow performs better (for at least one admin).

I've never actually used Piefed and most information I could find was three months old. If I missed anything important or made mistakes, please let me know in a reply.

Edit:

• Combines duplicate posts.
• User karma. Users with low karma get a flair.
• Comments with a score of -10 or lower get collapsed by default.