How to Generate Custom Forms with Builders in Rails

I have a Rails4 application for holding applications for different events.

The problem is, the application form of every single event need to have different fields. For some events I need to ask users for gender and for some events I need to ask users about their occupation. The application form structure for each event is quite different.

I have been able to deal with this problem with VisualFormBuilder when I was using Wordpress. VisualFormBuilder is a plugin which gives you flexibility when generating custom forms. You can just drag and drop the fields (inputs, selects, checkboxes etc.) you want and it will create the custom form for you.

What is the best way to do this kind of thing in Rails? Is there any GEMs available? Or what is the logic and strategy behind that?