I've always found Oman and the Ibadi faith interesting, but I haven't found a good short (or not so short) summary of their history. How exactly did they manage to survive when surrounded by nations that saw them as at best a different denomination, and at worst a continuation of the hated Kharijites?
Perhaps someone with more knowledge will provide additional details, but in the meantime let me point you to this excellent summary by /u/Labrydian : https://www.reddit.com/r/AskHistorians/comments/30hmfr/how_did_ibadi_oman_survive_under_the_caliphate/cptc3vd/