Controlling who can answer

Open and close on a schedule

Set an opening date, a closing date, or both. Before it opens the form says when it will; after it closes it shows your own message if you've written one.

Cap the responses

Set a maximum and the form closes itself once it's reached. The count is of stored responses, so the person who takes the last place gets in and the next one is turned away.

Password protection

A Pro feature. The password is a shared secret for a group, not a login — it's stored hashed, and someone who enters it correctly gets a signed cookie for that form.

Changing the password invalidates every cookie already issued, which is what changing a password should do.

Save and resume

A Pro feature. Respondents get a link that brings their answers back, which matters on anything long enough that nobody finishes it in one sitting.