Choice of Google Form Add-ons
One that I am really happy to see is "Choice Eliminator". It takes choices out of a list of multiple-choice, checkbox, or list entries. That way if one submitter selects an option, it is no longer available to people who have not taken the Form yet. I see this as an outstanding option for people that schedule appointments. The choices disappear so you don't double-book. Here is a website with tutorial of how to use Choice Eliminator - click here.
Create your Form. Go to the Add-ons store in the Add-ons menu and select the Choice Eliminator and try it out. This will be awesome for teachers scheduling conferences. Too bad it didn't come out a month ago.