Mostly interface, some say it is more simple. It does both the aggregation and communities like Lemmy and microblogging. It also does some sort of microblogging related to the individual communities but I don’t really understand how that feature works.
Somebody could use it instead of lemmy or mastodon, but it also federates to them so nobody misses out.
Beehaw defederated from some of the larger Lemmy instances due to problem users and limited moderation abilities (Lemmy as a platform, limited staff). As one of the larger Lemmy instances themselves and where many Reddit folks went, this rubbed some people the wrong way. Beehaw has a specific idea about the community they want and are proactive in protecting that vision, I don’t know how this makes them “corporate” but there you go.