From the website:

What is PHP Surveyor?

PHP Surveyor is a set of PHP scripts that interact with MySQL to develop
surveys, publish surveys and collect responses to surveys. Once a survey
has been created it can be published as an online survey (displayed as
single questions, group by group or all in one page) or you can use a
dataentry system for administration of paper-based versions of the survey.
PHP Surveyor can produced 'branching' surveys (set conditions on whether
individual questions will display), can vary the look and feel of your
survey through a templating system, and can provide basic statistical
analysis of your survey results.

PHP Surveyor includes the capacity to generate individualised 'tokens', so
if you have a list of people you want to invite to participate in a survey
you can issue each one with a token, and they will be able to access the
survey using that token. This allows for quite good quality control of
your surveys.

WWW: http://www.limesurvey.org/