My fiancée and I are getting married this year, and rather than giving out traditional RSVP cards, we decided to bring the whole process into the modern era and build a website containing all of the wedding details with an RSVP form (well, technically there are two). We didn’t envisage many people viewing the website on a computer, so this was designed mobile first with the BootStrap framework on a single page so that all information is readily available at all times.
There are 2 RSVP forms (one for day guests, one for evening guests) that submit the entered information into a MySQL database. We have asked for a few pieces of data such as meal choice, if the guest will be attending and what their favourite song is (so that we can tailor the wedding reception to include music that everyone enjoys!). The site is fully responsive (even to my massive 3440 x 1440 monitor) as expected these days, though the primary focus was on mobile users.