Activity for Cristal

What is the app that my guests can use to upload pictures of our wedding on? I have three different apps download and I don't know which one it was. LOL

What type of options did you give your guests to RSVP? What works the best? I can only think of RSVP cards that are put in the invitation and by email. Thank you!

Is there an app that my guests can download to share all the wedding photos they took on their phones with me? Thank you!