I'm Always Left Astonished!

So given lemm.ee is shutting down, what exactly is piefed

All ik is it’s a different “app” than lemmy but still communicates with it

PieFed is like Lemmy in the same way that Lemmy is like Reddit.
One thing I absolutely adore about PieFed is the focus on democratization of moderation: by putting the power to choose your own experience into the hands of the users, you reduce the burden of moderation, e.g. the reason that Lemm.ee is shutting down. For example a new user account that joined less than two weeks ago gets an icon next to the username, and accounts that post 10x more often than comment (unregistered bot?), and people who receive 10x more downvotes than upvotes (troll?), so at a glance you can get more of a feel what you are up against before or as you reply to someone.
I dislike how Lemmy is somehow more authoritian than Reddit itself: yes there is a modlog but no modmail, no notification sent about a moderation event, no ability to ask questions why, nor even acknowledgment as to which mod did the action so that you can tag them (without having to put the full list of mods) elsewhere. Moreover, I do not expect this to ever change, not in five years nor ten, and in fact this aspect of Lemmy has actually gotten worse over time - Lemmy after all was founded by the tankies who were kicked off of Reddit for being too toxic, then decided to make their own Reddit, with blackjack and hookers:-). Which they did, and kudos, and it's absolutely great to see... but tankies are well known for their authoritarianism, see e.g. admin practices on Lemmy.ml.
PieFed is already doing things that Reddit had not. The goal of Reddit was to increase shareholder profits, not improve end user experience. PieFed is the second non-tankie implementation of a true Reddit alternative, after Kbin/Mbin, but PieFed is under very active development and in many ways has already surpassed Lemmy. See it for yourself - e.g. every cross-post has all the comments combined across all of the cross-postings, and the categories of communities (user customizable and shareable btw) are adorable.
https://piefed.social/
Mobile app
Example cross-post showing all comments across all posts
- Ooh u might check it out then
  I really like about lemm.ee in the admins block illegal and spam instances then I’m free to block NSFW and bots myself. As for moderation stuff yeah I remember a whole controversy over people not wanting to donate to lemmy admins but also not wanting to fund their political views. As for the comments that sounds awesome, I like to lurk and browse comments that aggregation sounds awesome. Also completly forgot about mbin might check them out
Basically. Everything is still fediverse. Its just a different flavor. And has many benefits.
Think of it like web browsers.
You can visit websites using Firefox, or you can visit websites using Chrome. Websites all speak the same language, so both Firefox & Chrome can load them.
In the case of Lemmy & PieFed, they also speak the same language, in this case that language (or protocol) is called ActivityPub.
So if you use a Lemmy app, it can talk to the different Lemmy servers, but it can also talk to different PieFed servers. Similarly if you use a PieFed app, it can talk to the different PieFed servers, but it can also talk to Lemmy servers.
Now Lemmy & PieFed are not the exact same. In the same way British English and American English are not the exact same. So your Lemmy app might not let you login to a PieFed instance directly. But they are similar, so maybe one day.
Since you are a lemm.ee user, your instance is going away, so you'll need to pick a new instance. You can pick a Lemmy instance or a PieFed instance, but the one you pick may limit the apps your able to use. Both also have websites/web apps, so if you're happy with the web version, you can use that too.
I'll also add that PieFed has some features that Lemmy doesn't have. So if you pick PieFed you may get some new features. The downside may be that you can't use your favorite app anymore.
I suggest trying both, but it you're not sure or ready, you can just pick another Lemmy server. You can always try PieFed at a later date.
Basically a Python implementation of Lemmy, so they can talk to and share content with each other. Has different features and development priorities, which may or may not appeal to you.