It’s a Lemmy alternative. They aim to do more or less the same thing, but are made by different people and developed independently.
But thanks to federation, Lemmy and Kbin can communicate similar to how Lemmy and Mastodon can communicate. So you can simply use the one you like best, and not worry about missing out on content posted to Lemmy.
Kbin is rough around the edges as it’s earlier in development than Lemmy, but it has more features than Lemmy, like a “microblogs” tab so that you can use it like Mastodon/Twitter if you want.
Kbin is like Lemmy's twin brother. Lemmy and Kbin live in the same house (the Fediverse), but they live in separate rooms. However, they occasionally come into each other's room to hang out, eat pizza, and play video games together.
Lemmy is also slightly concerned about Kbin's magazine collections.
