I would love to be able to easily invite friends to events via SMS. I have a group of friends who come out to a regularly-scheduled hang-out, but we change up the location each week. It would be awesome if I could see who plans to attend.

I haven't been able to find anything like that yet (at least for iOS). I feel like it could probably be done with Twilio's API, but I'm a front-end developer and haven't really looked into it that much.