Kbin and Lemmy are different software that have communities (magazines on Kbin) where people post content and have threaded discussions. Very much reddit-like.

There are many instances of both Kbin and Lemmy.

Kbin and Lemmy do federate, i.e. ‘talk’ to each other via the same protocol. This means you can see and interact with content regardless which of the two software an instance has chosen. It’s not perfect, e.g. I believe some minor features are not compatible (yet) and I have experienced that federation doesn’t always work, but hopefully this all becomes smoother when both mature.