LimeSurvey

LimeSurvey is a powerful, open-source platform that can be self-hosted, offering complete data control. It supports unlimited surveys and responses, complex question types, and a wide array of plugins. It's ideal for tech-savvy users, universities, and organizations with strict data sovereignty needs. The core software is free.

It scores highly for its total cost of ownership, flexibility, and independence from SaaS limitations, though it requires more technical setup.