LimeSurvey

LimeSurvey – A powerful, open-source survey platform. A free alternative to SurveyMonkey, Typeform, Qualtrics, and Google Forms, making it simple to create online surveys and forms with unmatched flexibility. Maintained by LimeSurvey on GitHub, where it has earned 3,708 stars from the community.

It's actively developed around survey, limesurvey, php, and is a solid reference for anyone building with these tools.