There are not so many open source survey software. Many have tried to emerge, but only LimeSurvey succeed. This is the most powerful open source survey software available today. If you look at more than a full dedicated survey software (CMS, Community Management), look at Drupal. It has some nice webforms & survey abilities.
Leading open source survey software
LimeSurvey basically contains everything you need for doing nearly every survey with grace. LimeSurvey (former PHPSurveyor) has been used for years by thousands of web sites, and is the leading open source survey software.
Survey™ is a free web based survey and data entry forms software for processing & gathering data online.
Other open source survey software
JSurvey is a open source survey software for building online survey. It is based on Java (J2EE) technologies.
PHP scripts to let non-technical users create surveys, administer surveys, gather results, view statistics.
This module adds a webform nodetype to your Drupal site. Typical uses for webform are to create questionnaires, contact or request/register forms, surveys, polls or a front end to issues tracking systems.