I wonder what the federated version of r/place would look like. It should not be too hard to create a collaborative pixel board and accept input from anywhere in the fediverse. But we would need to come up with some cool fedi spin. A chessboard, maybe, where every server has a square?
In the future, when the fediverse is more mature, it would be cool to create something.
They are two separate projects with similar goals (implement a Reddit clone). They both use the activitypub protocol, so they can generally interoperate. Other activitypub based services, such as mastodon, can also interact with either Lemmy or kbin, but in a more limited and clunkier way.
Lemmy was started first so there are more servers and more users, kbin is more recent.