form-builder

This form builder is currently a standalone app which you can pick out the 
pieces you need for your app (I extracted it from a recent app).  Will package as a gem/generator soon with tests as that would be much more useful.

Basically, you can create forms with any number of fields.  Text boxes, text 
areas, check boxes, and select menus are currently supported.

When forms are submitted, their content is stored and can be optionally sent
to a selected email address.

For use in production, you'd need to add your own access controls.