To my knowledge, no others exist. You can look at flarum.today which catalogues most every Flarum extension out there. I only see one invite plugin, but maybe someone has made one and named it differently?
Hmm, looking at Github, seems like @Kyrne forked the invite plugin and did some work on it. You'll have to ask him (or maybe he'll appear now) if it's in working condition or not.
