Event organization has been fractured for some time. Folks in my area have been using Partiful[1]. Bash[2] (now theBash) used to be in this space a bit but they left. Facebook has even added the ability for people without facebook to attend events on Facebook (they get an interface that shows them the event details and lets them put a name in "on" the event that isn't connected to an account).
I think Partiful is pretty good at what it does - no ads, can specify reminders, manages text blasts. The problem, to me, is messaging - how do you tell people about a thing? We are all getting tons of spam texts all day. Apple can cheat here because they own iMessage so maybe they will win overall - but still, what about your android friends? Time will tell. Good luck to everyone organizing events.