Hexbear is an instance formed mostly by former r/chapotraphouse users after that sub was banned from Reddit a few years ago. Hexbear used to run on a custom fork of Lemmy so that the community could add extra features that they wanted (like custom emoji) but it was recently ported back to mainline Lemmy after merging or reimplementing as many changes as possible.
Currently, Hexbear does not have federation enabled, and there is discussion about who to federate with or even whether to federate at all. The community is very active and self-sufficient and some members prefer the isolation.
Content-wise, it's a leftist-focused instance. Some shitposts, some serious posts, and a lot of inside jokes.