Dave’s suggestion is the best if what you want is something like kbin, because it is, well, kbin but with work continuing on it.

A popular example mbin server, if you want to take a look:

http://fedia.io/

If you’re just looking for a compatible-with-lemmy-but-not-lemmy server, and not specifically in search for something like kbin:

Sublinks

https://demo.sublinks.org/

I thought that there was at least one other project, but damned if I can remember or find it.

EDIT: Right, piefed.

https://piefed.social/

If what you’re okay with lemmy, but don’t like the lemmy Web UI, then there are some alternative frontends. My own home instance runs several, which you can take a look at. A number of other lemmy instances also do so:

mlmym (a lookalike for old.reddit.com):

https://old.lemmy.today/

Photon (looks like it’s not working on my home instance ATM, so here’s lemmy.world’s):

https://photon.lemmy.world/

Voyager:

https://m.lemmy.today/posts/lemmy.today/all

Alexandrite:

https://alexandrite.lemmy.today/lemmy.today

slemmy:

https://slemmy.libdb.so/

leanish:

https://natoboram.github.io/Leanish/

lemmyBB: I don’t know of functioning instances running this, but they may be out there:

https://github.com/LemmyNet/lemmyBB