For our wedding I wrote an RSVP web app for invitees to respond. Given a unique invite URL people could enter their attendance for the ceremony and reception as well as log their dietary requirements.
The app was written in a couple days with Node, Mongo and some vanilla JS. The CSS and avatar images were thanks to the beautiful Semantic UI. It was hosted for a couple months on an Ubuntu VM and pointed at via a
.wedding top-level domain!
Check out the blog post for more on what was involved!