Ask YC: Choosing a web framework

You can easily modify KPAX (http://www.vimeo.com/1098656) to do what you need, and more. kpax is based on web2py (http://mdp.cti.depaul.edu) and you can download it from here (http://mdp.cti.depaul.edu/appliances/default/show/37).This (http://mdp.cti.depaul.edu/AlterEgo/default/show/99) shows how to add captcha. I will help you more if you sign up for the web2py google group.

rails

but you might have to modify it a little bit to allow non-account holders to modify data, sort of unconventional?

if you're looking for ease of use and speed, here, i'd suggest going with a framework on a language you already know well.

what languages would those be?

ruby, c, scheme, and ocaml

since you know ruby, i'd suggest ramaze, sinatra, merb or rails (in order of my preference)