This WordPress “plugin like” theme is useful to you if you want to make an RSVP and guestbook for your event, for example wedding or any other events.
It has admin setting page containing customizer form to change background image, form texts, text colors and so on.
Completely optimized for mobile browsers too.
But the interface is in Bahasa Indonesia, but you can play around with the settings easily, just try it.
The only thing that you must be careful about, is, this program is not really secure, I mean anybody can post a comment to it and you need to maintain and monitor who left comments, probably spammers, or random texts posters, you have to remove them manually.