Limit Form Responses

These techniques require the installation of scripts or Add-ons.  How to install an Add-on (on YouTube)

If you want to... ...you should use  

close a Form after a specific number of responses or at a specific time

formLimiter from New Visions Cloud Lab

formLimiter is now a Forms Add-on

How-to video on YouTube
 

allow only one person to select each option on a question (as in scheduling appointments)

or

allow a specified number of people to select an option (as in workshop sign-ups)


Choice Eliminator
 from EdListen Scripts

Instructions for using Choice Eliminator appear on the page linked above.  

Choice Eliminator is a Forms Add-on

How-to video on YouTube  (video updated on January 18, 2015 to show the new features of Choice Eliminator)
 


allow a specific number of responses for each option on a question

For most simple sign-up sheets, use Choice Eliminator.  If you need a more complicated set of rules for adding and removing options, use formRanger.  This option will require some understanding of spreadsheet functions.

some spreadsheet functions and formRanger from New Visions Cloud Lab

formRanger is now a Forms Add-on

See my documentation of the process and get a Sheet with formulas to use as a starting point