if you mean support system try PHPAskIt http://www.jooria.com/scripts/PHP-Guestbooks-98/PHPAskIt-839/index.html osTicket http://www.jooria.com/scripts/PHP-Customer-Support-113/osTicket-895/index.html and http://www.jooria.com/scripts/PHP-Customer-Support-113/Help-Center-Live-772/index.html
I understood you meant more like online customer surveys, that kind of thing. This was the first one I came up with: http://www.limesurvey.org/ - but I'm sure there are more.