Fediverse memes

As you're kind of implying by putting "app" in scare quotes, it's really an entirely separate platform. Any service that implements ActivityPub can theoretically access any part of the fediverse. There's a subset of the fediverse (sometimes called the threadiverse) which platforms like Lemmy and PieFed are built to work with, where you have threads organized into communities and up- and downvote stuff.

PieFed and Lemmy have largely similar goals in the sense that they're two ways to join and interact in the same threadiverse communities, but PieFed's development has been characterized by rapid growth, as indicated in the meme. This means it can do most or all of what Lemmy does, plus extra stuff that's exclusive to PieFed.

Right now, that means things like anonymous voting, de-duplication of posts (they get combined into a single post with separate comment sections of each repost), filtering of "bad" images (like in the Nicole gore saga), warning labels on link posts with unreliable sources, support for "topics" (like multireddits from the old place), a marker for consistently low-reputation users; basically, it's a bunch of quality-of-life stuff. In theory, rapid development could also mean things breaking more often, although I haven't seen any of that personally.

I'm commenting from Mbin, a whole separate platform again, so arguably I'm impartial. I don't have an account on either Lemmy or PieFed.