No first-hand experience, and arguably not really a cult, but I have a friend who's a recovering alcoholic, and according to him a few of the local AA groups around us have a few members who are in the weird fringes of the rationalist community, maybe sort of tangentially connected to the "zizians"

For those not familiar with the zizians, behind the bastards had a pretty decent series on them

There's also a decent amount of weird overlap between self help type groups like AA (not that AA isn't without plenty of valid criticism) and abusive cult-like organizations. I think the elan.school (Joe vs Elan School) webcomic touched on that, and I also recommend that as an interesting look into the troubled teen industry (trigger warnings for child abuse and such on that)